Finding a soft lock of my hair and twirling it around my fingers. Both for the softness and the gentle tugging at my scalp. And as a bonus it's fairly socially acceptable.
There's been a song stuck in my head for as long as I can remember (decades) that only comes out of the recesses of my brain when I'm alone, and I hum it over and over. Usually this is during driving or focusing on coding. Kinda frustrating that I don't even know if it's a real song or just something my brain is doing for fun. (It sounds a bit like the civil war song, When Johnny Comes Marching Home, I guess?) I'm too self-conscious to do it around other people.
As an adult it is a mix of leg jiggling and rubbing my finger nails against my thumbs. As a child I used to tap out rhythms with my heels and toes, much to the chagrin of my teachers and classmates.
When my feet are available for this, such as laying down or dangling, I like to push one down while pushing it up with the other foot, then switching feet.
Rotate left & right on my desk chair
Pacing around my living room puffing on my nicotine vape & talking to myself
Stroking my walrus mustace (I blame Jamie Hyneman lol)
Thumb to finger taps. I do this often, more when getting nervous. I tap teeth to each other, too, feeling like I'm tapping one top to one bottom at a time. Going all the way around to tap all my teeth. I realized I'm tapping multiple teeth each time, but it's a tap for each pair of teeth.
Usually when I notice I'm doing something (stroking my beard or moving my legs are the most common ones) and I have to be discreet, I try to focus on moving my toes
When COVID hit and I started working from home, I decided to try growing a beard. After all, I didn't need to look 100% presentable during that awkward phase when it looks like you just forgot to shave a few days in a row.
Now, it's become a permanent part of my face and I love stroking it or pulling at the hairs (not enough to pull them out, just enough to play with them).
I like putting pressure on the arch of my feet. (Or where my arch would be as I have extremely flat feet.)
I actually bought a small wooden foot massager for this. As I'm working, I can just put my feet on this and roll them back and forth. I get the sensory input that I'm craving without needing to stop working to find something to press my feet against.