Holding on to anger is like grasping a hot coal with the intent of throwing it at someone else; you are the one who gets burned.

Hatred does not cease through hatred but through love alone they cease.

There are three types of people in the world. What three? One who is like carving on a rock, one who is like scratching on the ground and one who is like writing on the water. What sort of person is like carving on the rock? Imagine a certain person who is always getting angry and his anger lasts long, jut as carving on a rock is not soon worn off by wind, water or lapse of time. What sort of person is like scratching on the ground? Imagine a certain person who is always getting angry but his anger does not last long, just as scratching on the ground is soon worn off by wind, water and lapse of time. And what sort of person is like writing on the water? Imagine a certain person who, even though spoken to harshly, sharply, roughly, is easily reconciled and becomes agreeable and friendly, just as writing on the water soon disappears.
Anguttara Nikaya I/283

Suppose an enemy has hurt you in his own domain, why should you annoy yourself and hurt your mind in your own domain?
Suppose someone, to annoy, provokes you to do some evil act, why allow anger to arise and thus do exactly as he wants you to do?
Visuddhi Magga

One day, Akkosaka heard that someone from his religion had converted to be a Buddhist monk. Enraged, he stomped off to curse the Enlightened One with harsh words in person. After letting off his steam, the Buddha had a calm conversation with him (as abridged) - 'Do friends come to you as guests?' 'Yes.' 'Do you serve them delicacies?' 'Yes, sometimes I do.' 'If they don't accept them, to whom do they belong?' 'They would be mine.' 'Likewise, that with which you have insulted me, I do not accept - it is all yours. Whoever returns insult to one who insults is said to be sharing company with that person, which I do not.'
Hearing this, Akkosaka assumed he was displeased, to which the Buddha replied, 'Where is anger from one free of anger, who has his mind tamed and equanimous, who is liberated with right understanding, who is tranquil? One worsens matters by flaring up at another who flared up. Whoever doesn't flare up at another doubly wins a battle difficult to win, benefitting oneself and the another. Understanding another's anger, one mindfully maintains one's peace. When one does so to heal the illness of anger for both, those who think one is a fool do not know the Dharma.' Hearing this, Akkosaka remarked at the magnificence of the Buddha's teaching, and ordained as a monk to learn from him, thereafer attaining Nirvana (as an Arahant)!
Akkosa Sutta

You will not be punished for your anger, you will be punished by your anger.

When reason ends, then anger begins. Therefore, anger is a sign of weakness.

If subconscious anger had a parallel in Buddhist writings, it would have to do with what is called mental unhappiness or dissatisfaction. This is regarded as the source of anger and hostility. We can see subconscious anger in terms of a lack of awarness, as well as an active misconstruing of reality.

If there are sound reasons or bases for the points you demand, then there is no need to use violence. On the other hand, when there is no sound reason that concessions should be made to you but mainly your own desire, then reason cannot work and you have to rely on force. Thus, using force is not a sign of strength but rather a sign of weakness. Even in daily human contact, if we talk seriously, using reasons, there is no need to feel anger. We can argue the points. When we fail to prove with reason, then anger comes. When reason ends, then anger begins. Therefore, anger is a sign of weakness."
from 'The Dalai Lama, A Policy of Kindness'

Some people feel that although it may be right to curb feelings of intense hatred which can cause us to be violent and even to kill, we are in danger of losing our independence when we restrain our emotions and discipline the mind. Actually, the opposite is true. Like their counterparts of love and compassion, anger and the afflictive emotions can never be used up. They have, rather, a propensity to increase, like a river flooding in summer when the snow melts, so that far from being free, our minds are enslaved and rendered helpless by them. When we indulge our negative thoughts and feelings, inevitably we become accustomed to them. As a result, gradually we become more prone to them and more controlled by them. And we become habituated to exploding in the face of displeasing circumstances.
Inner peace, which is the principal characteristic of happiness, and anger cannot coexist without undermining one another. Indeed, negative thoughts and emotions undermine the very causes of peace and happiness. In fact, when we think properly, it is totally illogical to seek happiness if we do nothing to restrain angry, spiteful, and malicious thoughts and emotions. Consider that when we become angry, we often use harsh words. Harsh words can destroy friendship. Since happiness arises in the context of our relationships with others, if we destroy friendships, we undermine one of the very conditions of happiness itself.
Ethics for the New Millennium

Question: What should you say to a loved one who is talking about a third person with hatred or anger? On the one hand, you want to show compassion for the feelings being experienced by the loved one. On the other hand, you don't want to reinforce or lend approval to that hatred. What might one say?
Dalai Lama: Here I would like to tell a story. Once there was a Kadampa master called Gampowa who had many responsibilities. One day he complained to the Kadampa master Dromtonpa that he had hardly any time for his meditation or for his Dharma practice. So Dromtonpa responded by agreeing with him, "Yes, that's right. I don't have any time either." Then once an immediate affinity was established, Dromtonpa skillfully said, "But, you know what I am doing is for the service of the Dharma. Therefore, I feel satisfied." Similarly, if you find one of your beloved ones speaking against someone out of anger or hatred, maybe your initial reaction should be one of agreement and sympathy. Then once you have gained the person's confidence, you can say, "But...."
Healing Anger: The Power of Patience from a Buddhist Perspective

Anger cannot be overcome by anger. If a person shows anger to you, and you show anger in return, the result is a disaster. In contrast, if you control your anger and show its opposite--love, compassion, tolerance, and patience--then not only will you remain in peace, but the anger of others also will gradually diminish. No one can argue with the fact that in the presence of anger, peace is impossible. Only through kindness and love can peace of mind be achieved.
...human beings can judge and reason; we understand consequences and think in the long term. It is also true that human beings can develop infinite love.... However, when humans become angry; all of this potential is lost. No enemy armed with mere weapons can undo these qualities, but anger can. It is the destroyer.
If you look deeply into such things, the blueprint for our actions can be found within the mind. Self-defeating attitudes arise not of their own accord but out of ignorance. Success, too, is found within ourselves. Out of self-discipline, self-awareness, and clear realization of the defects of anger and the positive effects of kindness will come peace.
How to Expand Love: Widening the Circle of Loving Relationships

Q: Can you discuss the problem of self-hatred, and the Buddhist means to alleviate it?
A: In fact, when I first heard the word "self-hatred" and was first exposed to the concept of self-hatred, I was quite surprised and taken aback. The reason why I found it quite unbelievable is that, as practicing Buddhists, we are working very hard to overcome our self-centered attitude, and selfish thoughts and motives. So to think of the possibility of someone hating themselves, not cherishing oneself, was quite unbelievable. From the Buddhist point of view, self-hatred is very dangerous because even to be in a discouraged state of mind or depressed is seen as a kind of extreme. Because self-hatred is far more extreme than being in a depressed state, it is very, very dangerous.
So the antidote is seen in our natural Buddha-nature--the acceptance or belief that every sentient being, particularly a human being, has Buddha-nature. There is a potential to become a Buddha. In fact, Shantideva emphasizes this point a great deal in the Guide to the Bodhisattva's Way of Life, where he states that even such weak sentient beings as flies, bees, and insects possess Buddha-nature, and if they take the initiative and engage in the path, they have the capacity to become fully enlightened. If that is the case, then why not I, who am a human being and possess human intelligence and all the faculties, if I make the initiative, why can't I also become fully enlightened? ...no matter how poor or weak or deprived one's present situation may be, a sentient being never loses his or her Buddha-nature. The seed, the potential for perfection and full enlightenment, always remains.
Healing Anger: The Power of Patience from a Buddhist Perspective

...there are generally two types of harm caused by others. One type is direct physical harm inflicted by others and consciously experienced by you. The other type is harm done to your material possessions, reputation, friendship, and so on. Though not directed at your body, these acts are also a type of harm. Let us say that a person hits you with a stick, and you feel pain and become angry. You don't feel angry toward the stick, do you? What exactly is the object of your anger? If it would be appropriate to feel angry toward the factor that impelled the act of hitting, then you should not be angry with the person but with the negative emotions that compelled that person to act. Ordinarily, however, we do not make such distinctions. Instead, we consider the person--the intermediary agent between the negative emotions and the act--as solely responsible, and we hold a grudge against him or her, not against the stick or the delusions.
We should also be aware that since we possess a physical body that is susceptible to pain when hit by a stick, our own body partly contributes to our experience of pain. Because of our body and its nature, we sometimes experience physical pain even when no external causes of pain are present. It is clear then that the experience of pain or suffering comes about as a result of interaction between both our own body and various external factors.
The Compassionate Life

Q: Let's say that someone makes you angry. Your natural response to being hurt, your immediate response, is to get angry.... You might think about the event later, even much later, and every time you think about it you become angry all over again. How would you suggest dealing with that kind of situation?

Dalai Lama: If you look from a different angle, then surely the person who caused this anger in you will have a lot of other positive aspects, positive qualities.

Q: But what about if you look for the positive angles of a person or event and can't find any?

DL: Here, I think, we would be dealing with a situation where you might need to make some effort. Spend some time seriously searching for a different perspective on the situation. Not just in a superficial way. But in a very pointed and direct way. You need to use all your powers of reasoning and look at the situation as objectively as possible.
For instance, you might reflect on the fact that when you are really angry at someone you tend to perceive them as having 100 percent negative qualities. Just as when you are strongly attracted to someone the tendency is to see them as having 100 percent positive qualities. But this perception does not correspond with reality. If your friend, who you view as so wonderful, were to purposely harm you in some way, suddenly you would become acutely aware that they aren't composed of 100 percent good qualities.
Similarly, if your enemy, the one you hate, were to sincerely beg your forgiveness and continue to show you kindness, it's unlikely that you would continue to perceive them as 100 percent bad. So, even though when you are angry at someone you might feel that the person has no positive qualities, the reality is that nobody is 100 percent bad. They must have some good qualities if you search hard enough. So, the tendency to see someone as completely negative is due to your own perception based on your own mental projection, rather than the true nature of that individual.
In the same way, a situation that you initially perceive as 100 percent negative may have some positive aspects to it. But I think that even if you have discovered a positive angle to a bad situation, that alone is often not enough. You still need to reinforce that idea. So you may need to remind yourself of that positive angle many times, until gradually your feeling changes.
Generally speaking, once you're already in a difficult situation, it isn't possible to change your attitude simply by adopting a particular thought once or twice. Rather it's through a process of learning, training, and getting used to new viewpoints that enables you to deal with the difficulty.
The Art of Happiness: A Handbook for Living

...hatred is compared to an enemy. This internal enemy, this inner enemy, has no other function than causing us harm. It is our true enemy, our ultimate enemy. It has no other function than simply destroying us, both in the immediate term and in the long term.
The Art of Happiness: A Handbook for Living