When the state is genuinely counterproductive to your goals, remind yourself of that while suppressing it. If you're worried about lashing out and yelling at people, try to redirect your anger towards your irritating endocrine system that was involved in you being angry even though you don't want to be. Pretending that reductionism implies more than it does is useful: the mantra "just because I'm in a physical state associated with anger doesn't mean I have to be angry" is pretty good for suppressing reactions.
This still holds when the people in question are harming you, as long as anger is genuinely counterproductive. I used this method when an opposing team was cheating and purposefully running out the clock during a Mock Trial scrimmage. I had every right to be angry, but my anger was only impairing my competitive ability, so I just told myself that I needed to shut down this anger, and even though I had trouble trying to tone down my physical reactions (heart rate), I managed to stay calm and compete well.
If the anger is partially productive, trying to suppress all of it will not work because you are incentivized to fail. Try to suppress the parts that are problematic, and tell yourself things like "I'm allowed to be angry in this situation, but I'm not allowed to have [problem-causing component of anger], because it's just counterproductive."
When the state is genuinely counterproductive to your goals, remind yourself of that while suppressing it.
Suppressing emotions is generally unhealthy. Living with suppressed anger is stressful. Either funnel the emotion into action or release it.
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