Many people feel uneasy about the emotion of anger. It feels uncomfortable and may cause change. However, there is a good time and place for anger.
God is angry at sin, and this is good. Sin in itself is the opposite of love and life. Sin is what we dread when we see it clearly, and it's good that God is against it. Being in Christ allows us to still be in relationship with God even though we are sinners saved by grace.
Like God's anger at sin, a person may become angry when someone or something that's beautiful to him or her is threatened. Anger could be a form of wanting to protect, and this is a good type of anger. It indicates that something is wrong and needs to be fixed. It is love for someone or something that makes us feel very strongly that we want to protect the person or thing.
Anger is good if it involves love or is in line with wanting what God wants.
Often anger goes wrong because it's anger due to pride. An example of bad anger is someone being angry that a friend has decided to not go to an event they're planning because of being sick. This friend who is sick is making the right choice to try to heal. The angry person is not being right because the wellbeing of their friend should be more important than their event being more full of people. It's loving to want a friend to heal. It's prideful to want a friend to suffer in order to look good.
Pride often is what makes anger bad. But it's not to be confused with standing up for one's rights. It's okay to be angry if someone is treating you badly if truly you should be treated better in the situation. It's right to want to flourish and do well--God wants that too (although sometimes we don't agree with God on what that looks like exactly) and if someone is intentionally harming that, it's good to feel very strongly that something is wrong and should be changed if possible.