T-Rex Arms?
When I was younger I used to hook my thumbs in my belt, or in my pants pockets. My mother used to scold me for it. I studies pictures in magazines and catalogs to find other things to do with my hands.
I discovered that a lot of catalogs pose their male models with a hand flat (like for a handshake) and partly inserted into the pocket.
Lately I find I use "arms akimbo" which basically means hands on hips.
I had a sister who was in a play in college - her director told everyone on one scene (where there were a lot of people on stage but one person had a long speech) to "find something to do with their hands". Specifically they were NOT to use the "Adam" pose (hands in front of private parts - like some paintings of Adam in the Garden of Eden supposedlu before the invention of clothing, but with a nod to modern sense of modesty) or the "Reverse Adam" which is basically the same pose but with the hands behind the waist instead of in front.
When I took karate I was taught a number of "ready" poses, which were designed to "look" casual, but be ready to defend yourself if attacked - yet not "look ready" and also not look threatening (which can "challenge" an adversary and provoke an attack). One was the "professor" or the "nutty professor" - one hand on the elbow of the other arm and one hand on your chin - looking thoughtful - but it is also very easy to move to a fighting stance from there, or to block an attack. Feet were also important for these "ready" stances, worst was two feet together and both pointing the same direction. Feet slightly apart, a bit wider than your shoulders and at an angle was better - and the "nutty professor" had his feet in a "tee" formation - at right angles with one foot roughly in the center of the other, feet apart about a foot (a few decimeters). A very solid formation even if pushed of hit from a variate of angles or positions, and can easily be changed into a fighting stance.
I also remember having to train myself to not leave my hands dangling from the wrists and instead ball them into fists, or keep them in my pockets.
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ADHD-I(diagnosed) ASD-HF(diagnosed)
RDOS scores - Aspie score 131/200 - neurotypical score 69/200 - very likely Aspie