On the contrary “of 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. Romans 12:20 (NIV)
To “heap burning coals” was to act of public repentance. Paul was saying that we should treat our enemies with kindness so that they will become ashamed and turn from their sins. The best way to get rid if enemies is to turn them into friends.