James 3:8-9

but no human being can tame the tongue. It is a restless evil, full of deadly poison. With it we bless our Lord and Father, and with it we curse people who are made in the likeness of God. 

This is an area where I really struggle. I am in regular prayer in this area because of the struggle. As James says it isn't right for blessings and cursings to come out of the same mouth. We have to do better.