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.
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.
I'm a hair twirler/puller, also nail biter. I have a fidget slider toy too, the one looking like two playing cards, but it has limited use in a setting where others need to concentrate. Rubik's cubes are nice in those scenarios, like a 2x2, quick solve, quick scramble, repeat
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.
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 love drumming my fingers on the table/desk. And I can tell by the sound when it's time to trim my nails, because the tapping sound of nails hitting wood sets my teeth on edge.
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)
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.
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.
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.