Anger is never without a reason, but seldom with a good one.

Anger always comes with an account of itself, and the account is usually the weakest part. Something did happen, and the reason you produce is a rapid, self-serving explanation assembled after the feeling arrived, which is why it sounds so convincing and holds up so poorly the next day. Having a reason and having a good one are different tests.

Put a gap between the feeling and the response wherever you can. Write down the reason while angry, read it the following morning, and see whether you would still sign it. Most of the time you will keep the grievance and drop the case you built for it.