No need to apologize Ad Intra. It is not easy not saying the things that are in our mind when we are angry. It got to the point where i had to excuse myself to go the bathroom where I cooled off.

Coming down hard on yourself and doing self harm only reinforces the cycle of hurt and guilt.

I can tell you two things I do. Write down the things that are on my mind in a notebook where no one is hurt.

And I practice this breathing counting exercise until I gain some self control and can even do the exercise when I am just starting to get upset.

Breathing exercise - relaxed breathing do not force it.
If you are feeling very anxious or angry or just want to calm down, you can try a breathing exercise that takes the attention away from the trigger of anxiety to a simple tool of counting breaths.

Find a comfortable position seated or laying down. Begin to relax your breathing. Silently count 1 on the inhale, and two on the exhale. Then silently count 3 on the inhale and 4 on the exhale. Continue up to 10 or until you lose the count then return to one. No judgement. I sometimes end up at 18 then smile and return to 1. The idea is to focus on the breath and the counting and not get sucked into the anxiety or anger trigger. Also works to quiet the mind.