I tend to live in my own little world, and so it is very rare when other people try to do things to me that would justify a need for vengeful actions. When they occur however, I tend to go very far towards making sure that this person is made an example of, to show what happens to people who dare try to disrupt my life. It largely depends upon what the other person actually did, but if their actions are very hostile, it could lead to me awakening a personal ferocity and determination few can comprehend. Usually the resulting act of vengeance is vicious enough that other people get the message, and so I have a long time of peace without worries. I think by now people have learned that this friendly and gentle person under normal circumstances can, when ired, turn into something that has a tendency for extreme action and a disregard for the pain inflicted upon those who sought to cause pain.
It feels very good to take a haughty arrogant jerk who thinks he has a right to force his views on others and to bring him to his utter ruin. I guess the challenge I face is that I need to gain better control of this, because otherwise I might develop a taste for looking for "monsters to destroy".
Edit: In some ways, I see myself performing this kind of role when it comes to dealing with bad people: