"Dearly beloved, avenge not yourselves, but rather give place unto wrath: for it is written, Vengeance is mine; I will repay, saith the Lord.
Therefore if thine enemy hunger, feed him; if he thirst, give him drink: for in so doing thou shalt heap coals of fire on his head."
This is instructive, and worded so that anyone would see the point. :) Instead of returning anger for anger, or misdeed for misdeed, we should step out of the way of wrath. When our enemies need something, we should provide what we can for them, and take care of everyone around us. The wording in the second verse makes it so that you could be happy to help your enemies even if you were still really mad at them, because you would be heaping coals on them... although I think that the real point of that, and of the first verse, is that God is the judge... he is the one who knows what he is doing, and his judgements are going to be a lot better than ours will be. I don't think it is about heaping coals on anyone, but just recognizing that God is a lot more clear-headed than we are... and that he has the right to judge, and we definitely don't.