Proverbs 25:21-22 If your enemy is hungry, give him food to eat; And if he is thirsty, give him water to drink; For you will heap burning coals on his head, and the Lord will reward you.

The Duke translation of this Proverb is “Be nice to those who are not nice to you, and God will bless your life.”
The problem is that this is so opposite of what the world teaches, and our flesh believes that we can hardly make ourselves do it as a lifestyle. The result is that we have a lot of conflicts, irritation, anger, bitterness, hurt feelings, and a whole lot of used-to-be friends.

The way to successfully make this behavior modification in ourselves is to memorize Proverbs 25:21-22 and meditate on it every day, and pretty soon, we will start to exercise self-control over our conversations and responses to people all day long, and God will keep His Word; he will reward.