The verse that comes to my mind about anger is:
Matthew 5:22 But I say unto you, That whosoever is angry with his brother without a cause shall be in danger of the judgment: and whosoever shall say to his brother, Raca, shall be in danger of the council: but whosoever shall say, Thou fool, shall be in danger of hell fire.
Cain had messed up, not Abel, so he had no real reason to angry unless it would have been at himself. Sometimes however there is "cause" to be angry, and you might be nuts if you weren't annoyed. If you really want to murder someone for annoying you, then you may have a problem.
There are some people who it seems almost enjoy rousing anger in others to throw them off. If they can get you to do something bad, they have a hold over you; and they can constantly remind you of it too. If you find yourself in that situation, realize that the anger you feel is rational; but expressing it would be irrational. Thus:
Ephesians 4:26 Be ye angry, and sin not: let not the sun go down upon your wrath:
When I get angry, I remember that verse and steel myself against acting unwisely. I get very cautious with what I say and do, lest I mess up. If I think someone is deliberately trying to provoke me, it used to bother me; now it amuses me. I won't let them win that way. There is another reason not to take the bait -- people will keep doing it if they get the reaction they want. Ha, don't let them win! Maybe they'll try something healthier.
There is an interesting verse in the Bible where the manuscripts vary widely. The usual translation reads "compassion."
Mark 1:41 And Jesus, moved with compassion, put forth his hand, and touched him, and saith unto him, I will; be thou clean.
Some manuscripts read "moved with anger." I think the original probably read "anger" and someone said that can't be right, so let me change that to "compassion." It is unthinkable that the original read "compassion" and copyists changed it to "anger."
I am not sure what could have made Jesus angry; but I assume, if he was angry, he had a good enough reason. The moral to the story is that he still did the right thing. He was able to be angry and sin not. When we see we are angry, it is like the Spirit talking to us the way God talked to Cain.
Genesis 4:7 If thou doest well, shalt thou not be accepted? and if thou doest not well, sin lieth at the door. And unto thee shall be his desire, and thou shalt rule over him.
Sin is out there like a beast ready to spring if we're not careful. Being aware of our emotional state when angry can become a blessing if we take it as a warning.
The urge to get angry is more often found in potentially strong people than weak ones. If they can master that urge, the way Peter did, it leads to realized strength.