"The destructive effects of hatred are very visible, very obvious and immediate. For example, when a strong or forceful thought of hatred arises, at that very instant it overwhelms one totally and destroys one's peace and presence of mind. When that hateful thought is harboured inside, it makes one feel tense and uptight, and can cause loss of appetite, leading to loss of sleep, and so forth.
If we examine how anger or hateful thoughts arise in us, we will find that, generally speaking, they arise when we feel hurt, when we feel that we have been unfairly treated by someone against our expectations. If in that instant we examine carefully the way anger arises, there is a sense that it comes as a protector, comes as a friend that would help our battle or in taking revenge against the person who has inflicted harm on us. So the anger or hateful thought that arises appears to come as a shield or a protector. But in reality that is an illusion. It is a very delusory state of mind.
Chandrakirti states in Entry into the Middle Way that there might be some justification for responding to force with force if revenge would help one in any way, or prevent or reduce the harm which has already been inflicted. But that is not the case because if the harm, the physics. injury or whatever, has been inflicted, it has already taken place. So taking revenge will not in any way reduce or prevent that harm or injury because it has already happened.
On the contrary, if one reacts to a situation in a negative way instead of in a tolerant way, not only is there no immediate benefit, but also a negative attitude and feeling is created which is the seed of one's future downfall. From the Buddhist point of view, the consequence of taking revenge has to be faced by the individual alone in his or he future life. So not only is there no immediate benefit, it is harmful in the long run for the individual.
However, if one has been treated very unfairly and if the situation is left unaddressed, it may have extremely negative consequences for the perpetrator of the crime. Such a situation calls for a strong counteraction. Under such circumstances, it is possible that one can, out of compassion for the perpetrator of the crime and without generating anger or hatred, actually take a strong stand and take strong countermeasures. In fact, one of the precepts of the Bodhisattva vows is to take strong countermeasures when the situation calls for it. If a Bodhisattva doesn't take strong countermeasures when the situation requires, then that constitutes an infraction of one of the vows.
In addition, as the Entry into the Middle Way points out, not only does the generation of hateful thoughts lead to undesirable forms of existence in future lives, but also, at the moment that strong feelings of anger arise, no matter how hard one tries to adopt a dignified pose, one's face looks rather ugly. There is an unpleasant expression, and the vibration that the person sends is very hostile. People can sense it, and it is almost as if one can feel steam coming out of that person's body. Indeed not only are human beings capable of sensing it, but pets and other animals also try to avoid that person at that instant.
If we examine how anger or hateful thoughts arise in us, we will find that, generally speaking, they arise when we feel hurt, when we feel that we have been unfairly treated by someone against our expectations.
These are the immediate consequences of hatred. It brings about a very ugly, unpleasant physical transformation of the individual. In addition, when such intense anger and hatred arise, it makes the best part of our brain, which is the ability to judge between right and wrong and assess long-term and short-term consequences, become totally inoperable. It can no longer function. It is almost as if the person had become crazy. These are the negative effects of generating anger and hatred. When we think about these negative and destructive effects of anger and hatred, we realise that it is necessary to distance ourselves from such emotional explosions. Insofar as the destructive effects of anger and hateful thoughts are concerned, one cannot get protection from wealth; even if one is a millionaire, one is subject to these destructive effects of anger and hatred. Nor can education guarantee that one will be protected from these effects. Similarly, the law cannot guarantee protection. Even nuclear weapons, no matter how sophisticated the defence system may be, cannot give one protection or defend one from these effects. The only factor that can give refuge or protection from the destructive effects of anger and hatred is the practice of tolerance and patience."

~ The Dalai Lama from Healing Anger: The Power of Patience from a Buddhist Perspective:

Question: Where does hatred come from?

Answer: That is a question which requires long hours of discussion. From the Buddhist viewpoint, the simple answer is that it is beginningless. As a further explanation, Buddhists believe that there are many different levels of consciousness. The most subtle consciousness is what we consider the basis of the previous life, this life, and future lives. This subtle consciousness is a transient phenomenon which comes about as a consequence of causes and conditions. Buddhists have concluded that consciousness itself cannot be produced by matter. Therefore, the only alternative is to accept the continuation of consciousness. So that is the basis of the theory of rebirth.

Where there is consciousness, ignorance and hatred also arise naturally. These negative emotions, as well as the positive emotions, occur right from beginningless time. All these are a part of our mind. However, these negative emotions actually are based on ignorance, which has no valid foundation. None of the negative emotions, no matter how powerful, have a solid foundation. On the other hand, the positive emotions, such as compassion or wisdom, have a solid basis: there is a kind of grounding and rootedness in reason and understanding, which is not the case with afflictive emotions like anger and hatred.

The basic nature of the subtle consciousness itself is something neutral. So it is possible to purify or eliminate all of these negative emotions. That basic nature we call Buddha-nature. Hatred and negative emotions are beginningless; they have no beginning, but there is an end. Consciousness itself has no beginning and no end; of this we are certain.

HOW TO TAKE INSULT

From: TheDailyEnlightenment.com Weekly 21/04/05:

On one occasion, the Buddha was invited by the Brahmin Bharadvaja for alms to his house. As invited, the Buddha visited the house of the Brahmin. Instead of entertaining Him, the Brahmin poured forth a torrent of abuse with the filthiest of words. The Buddha politely inquired:

"Do visitors come to your house, good Brahmin?"
"Yes," he replied.
"What do yu do when they come?"
"Oh, we prepare a sumptuous feast."
"What do you if they refuse to receive the meal?"
"Why, we gladly partake of them ourselves."
"Well, good Brahmin, you have invited me for alms and entertained me with abuse which I decline to accept. So now it belongs to you."
~ From the Akkosa Sutta ~

The Buddha did not retaliate but politely gave back what the Brahmin had given Him. Retaliate not, the Buddha advised. "Hatred does not cease through hatred but through love alone they cease."

PATIENCE - THE MAIN ANTIDOTE

Patience is the main antidote to anger. As common wisdom says: just count to 100... During this time, any of the below methods can be effective. The most effective method will depend on the actual situation. Especially in our age of rush and intense change, patience may not be seen as a positive quality, but take a minute to think impatience can easily give rise to a general feeling of anger.

Patience is like a beautiful ornament. When you become a person with great patience, it brings a certain element of charm to your life. You are loved by others, and you give no problems to your friends. You bring an element of joy, happiness, and calmness to other people's lives - your friends, your family, and the community. You do not have to ask to be accepted; everyone longs for your presence. Everyone looks up to you and respects you, not because you have worked for that or expected it, not because you were competing for their favor, but simply because of the nature of patience. You are respected and trusted, and you acquire dignity with the practice of patience. When you are honored, it is with sincerity, and it is something you can live up to.

...Just hearing about patience does not mean you are experiencing it now or will easily develop it. To lay the ground for training the mind, you must first tame the mind. To tame the mind, it is extremely important to do the basic shamata [tranquility meditation, calm abiding] practice, which develops calmness and tranquility. Then you can add the practice of patience, understanding the benefits of patience and reminding yourself to take advantage of the available antidotes.

~ From Dharma Paths by Ven. Khenpo Karthar Rinpoche ~