No it is not so. You can express your anger. But, your anger should not develop into hatred towards the person you are angry about. You should not continue to feel angry.
Once the anger has served its purpose, you should forget about it.
When you alight/get down from the bus you are travelling, you will not be running behind it.
In the same way, once you have expressed your emotion, you should not keep thinking about it. The reason being, if you stay with an emotion for a long time, your body will get affected.
Unpack your anger: http://wp.me/ptUIO-46
A Brief on Bach Flower Remedies: http://wp.me/ptUDl-7E