That cuts two ways for you. Yours is showing when you are sure you are hiding it, and people answer what they see rather than what you meant. And when you catch it on somebody else, your body has already responded before you decided anything, which is worth remembering before you treat that response as evidence.

Before you answer the face, get one piece of actual information. Ask what is going on, or simply wait for their first sentence and listen to it. Most frowns turn out to be a headache, a message they just read, or plain concentration.

Use it as a handle rather than as proof. Next time you catch yourself furious, try the word anguish instead and see whether anything in you agrees. If it does, you have found the layer that is worth attending to, and you found it with a word rather than an hour of analysis.

Which means the thing you have been calling a character flaw is closer to a skill nobody taught you. That changes the job: not becoming a person who never gets angry, but getting better at the ten seconds after it arrives. Skills improve with practice in a way that verdicts about your character never do.

A surprising amount of anger is really the protest that this should have come later, or with warning, or to somebody else. Drop the expectation of warning and the unfairness thins out, because there was never a version where you got told in advance. What is left is the actual problem, usually smaller than the outrage about its timing.