Jesus was clearly angry, when he turned over the bales, when he cursed the fig tree, when he called the Pharisees snakes and white-washed tombs. If Jesus got angry, and if God can at times be called a wrathful God, then it seems to me that getting visibly angry can't possibly be a sin. It must have purpose in God's plan for us. There must be some good that can come out of heated, angry encounters. It seems to me that some level of anger is almost a prerequisite for the making of Justice in the world.
Anger brings huge amounts of energy that can be used to change things.
One angry person can change the opinion of an entire even tempered mob. It wasn't until African-Americans became enraged with the Jim Crow laws and this country took to the streets in protest that major civil rights legislation was enacted. Sometimes it takes one spouse to get angry and dig in their feet and stand their ground before any changes get negotiated in a marriage. Anger can be a powerful tool for change. The key is training yourself what to grow angry at.