Anal Sphincter Release
There is no coincidence we have expressions like "tight ass" or "anal retentive." Most people walk around with their anal sphincters clenched. This tightens innumerable other muscles especially the jaw and neck.
Squeeze tight your anus (anal sphincter). Notice what else tightens: your back and thighs. Do it again and see if you can feel tightening in your jaw; squeeze as tight as you can and see if your teeth clenched.
Most people find it is impossible to be angry when their sphincter is relaxed. By keeping the sphincter relaxed, the pathway from your nose and mouth to your anus is open. The anus is the end of this pathway.
To quickly calm yourself, relax the anal sphincter.
For most people, clenching the anal sphincter is an old habit deeply ingrained. It may well take hundreds of times of consciously letting it go before it becomes a habit.
However, every time you do so, your body will relax and even if it lasts only for a few seconds, it is more relaxation than you usually give your body, so it is well worthwhile.