The mouth is the well spring of the heart. When people are thinking hateful thoughts, they feel angry and then say angry things. The best way for a person to stop saying angry things, is to stop thinking angry things. All feelings and words begin with our thoughts. Thoughts turn into feelings and eventually come out of our mouths or in our actions. The answer is to confess out bad thoughts as sin and ask God to help us think the right things. This way the problem is being corrected at its very inception.