Sometimes we have the right to be angry, but no one wins if we're cruel.
Christ never said following Him would be easy. Whether you are dealing with a mean-spirited action, (or just a bad situation) remember what Christ went through for you. God loves you and He empathizes with your situation. So be angry if you need to, but be strong and remember to focus on Christ, so you don't take your frustrations out on others.
An angry man stirs up dissension, and a hot-tempered one commits many sins.