"Anyone can become angry-that is easy.But to be angry with the right person, to the right degree, at the right time, for the right purpose and in the right way-that is not easy." -Aristotle
It's perfectly fine to be angry with the things that should arouse our ire. Racial violence, torture, genocide, child abuse, drug and sex trafficking, divorce, low educational standards, greed, adultery, pornography, and assaults on your faith all come to mind as being topics we can define as being displeased selflessly. None of the above have a selfish motive, and that's the qualifier to righteous anger. If you find yourself angry because your neighbor doesn't keep his lawn at an acceptable standard that pleases you, reread the frist line of this post.
While anger itself isn't always wrong, anger for a selfish motive is. We don't have a license to lose our temper with people who annoy us, but we do have an obligation to show displeasure with the things God hates for the reason God hates them. The anger that mars our fallen world is a self centered agenda, not a God centered one. So check your anger, is it aimed at those who dehumanize, mistreat, or denigrate others, or are we simply rationalizing that we're not getting what we want? It's not our responsibility to point the finger outward first, but to look inward to insure we are not contributing to the problem. If other people's sin angers you more than your own, it's time for a check-up from the neck up! And lastly
"Be angry and do not sin; do not let the sun go down on your anger, and give no opportunity to the devil."- Ephesians 4:26-27