"Delusions are states of mind which, when they arise within our mental continuum, 
leave us disturbed, confused and unhappy. 
Therefore, those states of mind which delude or afflict us 
are called 'delusions' or 'afflictive emotions'."
His Holiness the Dalai Lama

THE FEELING AGGREGATE

"Monks, there are beings who suffer not from disease of body for 1 year, for 2 years… even for 100 years. But it is hard to find in the world beings who can admit freedom from mental disease even for one moment, save only those who have destroyed delusions." 
The Buddha [Anguttara Nikaya (A.II:143); Samyutta Nikaya (S.III.:2)]

 Buddhist psychology describes four Mental Aggregates: Feeling, Discrimination, Primary Consciousnesses (5 senses and mental awareness) and the other aspects, gathered as the Compositional Factors.

The Feeling Aggregate is defined as 'an omnipresent factor of the mind which labels experiences into three categories: pleasant, unpleasant or neutral':

• When the label of pleasant is given to an object, we develop attachment.
• When the label of unpleasant is given to an object, we develop aversion, and sometimes even anger or hatred.
• When the label of neutral is given to an object, we often don't care about the object or even ignore it.

The process of labelling by the Feeling Aggregate usually only takes a fraction of a second. After applying the label, we tend to create a static opinion and image of the object in our mind. At this stage, the seed for prejudice is usually planted. Once we have established the opinion that something is pleasant or unpleasant, we often need a large amount of evidence before we are willing to change our mind – that is, if we are prepared to change our mind at all. 
Once we labelled an object unpleasant or bad, it appears as if the object is all bad by itself, as if badness is an inherent quality. We may label a person "bad", but the friends of this person would certainly not agree! 
Therefore, we need to realise that "good" and "bad" are merely subjective opinions of our mind, and the opinion is often founded on nothing more than a first glance and an almost automatic label. Things and people change quicker than our labels! Everyone tends to prejudice. Labelling is a convenient way to quickly make some sense of our surrounding world by categorising things in being "good" or "bad" to us. The main problem is that we tend to react to the world merely via these (over) simplified labels.

A practical example to reflect on would be medicines: most of them are poisonous in a large dose, but can still be healing in small doses. Every living being requires salt to live, but try eating half a kilo of it, and no doctor can prevent your speedy death.

From Chagdud Rinpoche's 'Gates to Buddhist Practice':

"To understand how delusion arises, practice watching your mind. 
Begin by simply letting it relax. Without thinking of the past or the future, without feeling hope or fear about this thing or that, let it rest comfortably, open and natural. In this space of the mind, there is no problem, no suffering. 
Then something catches your attention–an image, a sound, a smell. Your mind splits into inner and outer, self and other, subject and object. In simply perceiving the object, there is still no problem. 
But when you zero in on it, you notice that it's big or small, white or black, square or circular; and then you make a judgment– for example, whether it's pretty or ugly. Having made that judgment, you react to it: you decide you like it or don't like it. That's when the problem starts, because "I like it" leads to "I want it." We want to possess what we perceive to be desirable. Similarly, "I don't like it" leads to "I don't want it." If we like something, want it, and can't have it, we suffer. If we don't want it, but can't keep it away, again we suffer. Our suffering seems to occur because of the object of our desire or aversion, but that's not really so — it happens because the mind splits into object-subject duality and becomes involved in wanting or not wanting something. 
We often think the only way to create happiness is to try to control the outer circumstances of our lives, to try to fix what seems wrong or to get rid of everything that bothers us. But the real problem lies in our reaction to those circumstances. What we have to change is the mind and the way it experiences reality."

From The Art of Happiness: A Handbook for Living by His Holiness the Dalai Lama and Howard C. Cutler:

"We can see that there are many ways in which we actively contribute to our own experience of mental unrest and suffering. Although, in general, mental and emotional afflictions themselves can come naturally, often it is our own reinforcement of those negative emotions that makes them so much worse. For instance when we have anger or hatred towards a person, there is less likelihood of its developing to a very intense degree if we leave it unattended. However, if we think about the projected injustices done to us, the ways in which we have been unfairly treated, and we keep on thinking about them over and over, then that feeds the hatred. It makes the hatred very powerful and intense. Of course, the same can apply to when we have an attachment towards a particular person; we can feed that by thinking about how beautiful he or she is, and as we keep thinking about the projected qualities that we see in the person, the attachment becomes more and more intense. But this shows how through constant familiarity and thinking, we ourselves can make our emotions more intense and powerful. 
We also often add to our pain and suffering by being overly sensitive, overreacting to minor things, and sometimes taking things too personally. We tend to take small things too seriously and blow them up out of proportion, while at the same time we often remain indifferent to the really important things, those things which have profound effects on our lives and long-term consequences and implications.
So I think that to a large extent, whether you suffer depends on how you respond to a given situation."

SOME NOTES ON HABITUATION

On top of the above problems related to labelling, the aspect of habituation comes in to reinforce our opinions and prejudices. Strictly spoken, habituation is not negative; in fact it can be extremely positive. Note that the Tibetan word for meditation means "habituation". However, within the context of problematic emotions, habituation can cause exponential growth of problems. If we just look at the results of racial and religious discrimination and hatred, it is sadly obvious how extreme opinions can arise and create havoc, simply because they have become habitual. Once something is a habit, we do not question our behaviour anymore, it becomes automatic and extremely hard to change.

A story by the Buddha to illustrate habituation and the resulting closed-mindedness:

"A young widower, who loved his five year old son very much, was away on business when bandits came who burned down the whole village and took his son away. When the man returned, he saw the ruins and panicked. The took the burnt corpse of an infant to be his son and cried uncontrollably. He organised a cremation ceremony, collected the ashes and put them in a beautiful little bag which he always kept with him.
Soon afterwards, his real son escaped from the bandits and found his way home. He arrived at his father's new cottage at midnight and knocked at the door. The father, still grieving asked: "Who is it?" The child answered, it is me papa, open the door!" But in his agitated state of mind, convinced his son was dead, the father thought that some young boy was making fun of him. He shouted: "Go away" and continued to cry. After some time, the child left. Father and son never saw each other again."  After this story, the Buddha said: "Sometime, somewhere, you take something to be the truth. If you cling to it so much, even when the truth comes in person and knocks on your door, you will not open it."

Or, in terms of our general attitude, His Holiness the Dalai Lama notes in "Beyond Dogma – The Challenge of the Modern World":

"We all know that on days when we are in a good mood, when the whole world seems to be smiling at us, we can accept predicaments or bad news more easily than if our mind is already upset, frustrated or troubled, when the slightest incident might cause us to explode with negative emotions. If we make a habit of being governed by these negative emotions, we will lose our appetite, sleep badly, perhaps become ill, and lose a few years of our life as a result. So mental calmness is very important."

THE THREE POISONS

The three most important negative mental attitudes or delusional emotions are called the Three Poisons, these are anger,attachment and ignorance. Underlying all negative emotions are one or more of these three, with ignorance at the bases of all negative emotions (see also the page on mind). Ignorance here, mainly refers to the Buddhist concept of lack ofwisdom, or insight into the actual way that things exist.

His Holiness the 7th Dalai Lama (from 'Songs of spiritual change' translated by Glenn Mullin) wrote on attachment and anger:

"Merchants come from the north and south,
To gather in the trading center;
But after three days have passed,
Each goes his separate way.
Meeting for but a flash in time,
They should avoid fights and fancies.

Hooked by karmas from previous lives,
Love and hatred run fierce,
But soon we all go our own ways,
And each takes his suited rebirth.
Right now abandon interpersonal discrimination
Made on the basis of attachment and aversion."

HOW TO TRANSFORM NEGATIVE EMOTIONS

Sogyal Rinpoche writes in Glimpse of the Day:

"Two people have been living in you all your life. One is the ego, garrulous, demanding, hysterical, calculating; the other is the hidden spiritual being, whose still voice of wisdom you have only rarely heard or attended to. As you listen more and more to the teachings, contemplate them, and integrate them into your life, your inner voice, your innate wisdom of discernment, what we call in Buddhism “discriminating awareness,” is awakened and strengthened, and you begin to distinguish between its guidance and the various clamorous and enthralling voices of ego. The memory of your real nature, with all its splendor and confidence, begins to return to you.

You will find, in fact, that you have uncovered in yourself your own wise guide, and as the voice of your wise guide, or discriminating awareness, grows stronger and clearer, you will start to distinguish between its truth and the various deceptions of the ego, and you will be able to listen to it with discernment and confidence."

Poisonous 
By Jeniffer Edwards

Why cling to the arrows shot at you? 
Insults 
Wounds 
Time heals you see. 
Why hold so tightly 
Do these things define you? 
Do these things set you free? 
Why inject yourself with these poisons of the mind 
Anxiety 
Greed 
Anger 
Despair 
Why not let them go 
Set them free. 
Accept the choices you have 
And your responsibilities. 
Accept all that is, rather than "as it should be" 
For what does define "you" 
What will set you free 
What if you never find great meaning 
What if, in not clinging, 
You find stillness 
Calm 
Honesty 
Health 
Peace

In the Tibetan tradition, the most basic method to reduce our negative emotions is via analytical meditation. The reasoning is that the negative emotions are delusions – misunderstandings of reality. If one analyses the process of how they come about, we can discover where real problem lies. Analytical meditation appears a very good method, as one avoids emotional excitement in meditation, and very calm observation of the workings of our own mind usually presents answers quite easily.

So, simply by being calm and quiet, analyze what is behind these destructive emotions and learn where the fault really lies. In Buddhism, the fault never lies ultimately with the outside world! As all our positive and negative experiences are results of our own karma, only our failure to behave more positive causes us problems.

One of the biggest obstacles to rid ourselves of these delusions is habituation. Although it is possible to analyse afterwards why it may have been unjust to become angry at someone, it is not simple to stop oneself before anger comes up. More pages on specific negative emotions and how to deal with them are given under the heading of Delusional Emotions in the top left corner of this page. The 'Summary' page describes the general approach in detail.

It should be noted that the ultimate antidote to negative emotions is the wisdom of emptiness. As all distinctions of 'self' and 'other' vanish with this realisation, when all duality vanishes, things like good and bad, or pleasant and unpleasant become meaningless. Due to the way our mind works, it is quite difficult to make this wisdom 'breakthrough', and analytical meditation is a good starter to work on our day-to-day negative emotions and actions.

"This is the radical discovery of Buddhist psychology. You don't have to resign yourself to ordinary suffering, to being always unconscious of what is really going on, helpless before not only society and space and time and others, but more importantly before your own inner drives, impulses and demands. You need not give up and allow yourself to be buffetted here and there by passions and angers. You can become conscious of what you were formerly unconscious. You can understand your drives, see where they come from, block the source, and divert the energy for your own use. You can resist all imperatives and learn to wield the underlying energies. You can reclaim those energies for your life, for your happiness and the happiness of your loved ones."
Robert Thurman from "Anger"

In the way that a gardener knows how to transform compost into flowers, 
we can learn the art of transforming anger, depression, and racial discrimination into love and understanding.
This is the work of meditation.
Thich Nhat Hanh from "Touching Peace"

Instead of analysis, one can also learn to deal with negative/problematic emotions by practicing awareness of them, for a brief introduction see eg. the introductory article The Second Arrow: The Practice of Emotional Awareness, by Ken Jones. In fact this is a form of Vipassana whereby one focuses on emotions and feelings rather than eg. the sensations of the body. 
The basic instruction is simple: 'just observe', but to actually do that is a different story altogether, as we need to stay on the subject and not end up in endless conversations with ourselves. These kind of awareness practices form a major part of the Theravada tradition (with which I have limited experience, and therefore cannot elaborate much about).

IS IT POSSIBLE TO RID OURSELVES COMPLETELY OF DELUSIONAL EMOTIONS?

This is actually a unique feature of Buddhist psychology: everyone can basically become a Buddha. A Buddha can be defined as a sentient being who has no negative (delusional) aspects of mind, and who has developed all positive aspects of mind to the greatest possible extent. So, as a Buddha has no delusional emotions at all, and we can all become a Buddha, it is logical that we can all rid ourselves of delusional emotions that are the basic cause of all our suffering.

As His Holiness the Dalai Lama explains in Healing Anger: The Power of Patience from a Buddhist Perspective :

What premises or grounds do we have for accepting that mental afflictions can be ultimately rooted out and eliminated from our mind? 
In Buddhist thought, we have three principal reasons for believing that this can happen. 
One is that all deluded states of mind, all afflictive emotions and thoughts, are essentially distorted in their mode of apprehension, whereas all the antidotal factors such as love, compassion, insight, and so on not only are undistorted, but they also have grounding in our varied experience and in reality.
Second, all these antidotal forces also have the quality of being strengthened through practice and training. Through constant familiarity, one can enhance their capacity and increase their potential limitlessly. So the second premise is that as one enhances the capacity of these antidotal forces and increases their strength, one is able to correspondingly reduce the influences and effects of delusory states of mind.
The third premise is that the essential nature of mind is pure; in other words, there is the idea that the essential nature of mind is clear light or Buddha-nature.
So it is on these three premises that Buddhism accepts that delusions, all afflictive emotions and thoughts, can be ultimately eliminated through practice and meditation.

This is where Buddhist psychology departs from general modern-style psychology, which is aimed at reducing our problematic emotions to an 'acceptable level', until we can fit into society without too much trouble. The Buddhist idea that our mind can be totally free from attachment, aversion and ignorance, and all derived negative feelings and problems gives a totally different outlook on what we can achieve. The only problem is of course that we need to make a lot of effort to develop our minds to reach this perfect state of Buddhahood.