Seems to me a verse from Romans 12:20 is appropriate here: "If your enemy is hungry, feed him; if he is thirsty, give him something to drink. In doing this, you will heap burning coals on his head." You could also add a nice label on the back with a verse like this one: "For, whoever would love life and see good days must keep their tongue from evil and their lips from deceitful speech." I Peter 3:10