Charles Spurgeon once quoted that "Anger is temporary insanity" and in some sense I have to agree with him. When we get angry we usually loose control of the situation or someone has gotten us so mad we loose it and blow up.
I think we all vent sometimes and I think that is ok. We should have the freedom to say how we feel but, when that venting crosses the line and turns into anger then I think that is sin. God does bring things into our lives to help us grow in grace and I believe sometimes He allows situations to happen to us to test our walk. I mean how do we grow in grace if life was just plain easy. The grestest growth in a christian's walk is when a trial comes into our life and we deal with it like Christ would. We can learn so much by, like I said in my previous post by "Waiting on the Lord"
Anger never solves anything! What we need to do is focus on Christ and maybe ask Him, "Why He has brought this into my life and what can I do to deal with it without getting angry?"
Now saying all that, I think sometimes we are justified for being angry. I think when we see someone being hurt or abused, we have a right to be angry. But, even then we can use the situation to bring glory to God by the way we react. Seeing someone hurt a little child get's me riled up, I can not understand the abuse of a child that can not deffend themselves, so that would be tough for me.
I know when I have anger on my heart, I find it very hard to sleep. It eats at me, it causes me to not be in full fellowship with the Lord or with the person I am angry at. The bible teaches us not go to sleep until we have resolved our anger.
Be ye angry, and sin not: let not the sun go down upon your wrath: Neither give place to the devil. (Ephesians 5: 26-27)
He that is slow to anger is better than the mighty; and he that ruleth his spirit than he that taketh a city. (Proverbs 16: 32)
The Lord is merciful and gracious, slow to anger, and plenteous in mercy. He will not always chide: neither will he keep his anger for ever. He hath not dealt us after our sins; nor rewarded us according to our iniquities. (Psalm 103:8-10)
A soft answer turneth away wrath: but grievous words stir up anger.--(Proverbs 15:1)
A few good quotes on anger.....
An angry man opens his mouth and shuts up his eyes.
A truly humble man is sensible of his natural distance from God; of his dependence on Him; of the insufficiency of his own power and wisdom; and that it is by God's power that he is upheld and provided for, and that he needs God's wisdom to lead and guide him, and His might to enable him to do what he ought to do for Him.