Romans 12:17-20 (ESV)
17 Repay no one evil for evil, but give thought to do what is honorable in the sight of all.
18 If possible, so far as it depends on you, live peaceably with all.
19 Beloved, never avenge yourselves, but leave it to the wrath of God, for it is written, “Vengeance is mine, I will repay, says the Lord.”
20 To the contrary, “if your enemy is hungry, feed him; if he is thirsty, give him something to drink; for by so doing you will heap burning coals on his head.”
Much easier said than done. 🙁