Matthew 5:38-42
“You have heard that it was said, `An eye for an eye and a tooth for a tooth.’ But I say to you, Do not resist one who is evil. But if any one strikes you on the right cheek, turn to him the other also; and if any one would sue you and take your coat, let him have your cloak as well; and if any one forces you to go one mile, go with him two miles. Give to him who begs from you, and do not refuse him who would borrow from you.
Homily:
“Do not repay anyone evil for evil. Be careful to do what is right in the eyes of everyone. If it is possible, as far as it depends on you, live at peace with everyone. Do not take revenge, my dear friends, but leave room for God’s wrath, for it is written: “It is mine to avenge; I will repay,” says the Lord.” – Romans 12:17-19
You actually do your enemy a favor when you take vengeance into your own hands.