I get treated all kinds of funny, but a tattoo shop is about the only public place I feel OK- probably doesnt hurt that its one of my special interests and ive been doing it for about 20 years now. I have fairly severe aspergers/HFA- i can go days without speaking, I dont look at people, I talk way too loud when I do and ramble when I get going. I also tap patterns with my fingers (yngwie Malmsteen arpeggios) and feet and sway, but only when Im standing. I find that I need a "script" to deal with social interactions and when I dont have one and something unexpected happens I shut down completely. I've got a pretty good script for tattoo shops- I have alot of them, I have read just about every book out there and am pretty steeped in the history, plus at this point I know alot of people in the business and tend to just get tattooed by people I know or friends of friends so to speak... I'm also pretty upfront about the difference and people in shops are usually interested rather than put off. I find that I am able to sit like a rock because i can focus my mind down to one thing (sitting still) very easily. Unfortunately I do tend to get bad hives from anxiety which can be a serious problem but I manage it with medication, sometimes successfully. Case in point last month I was up in DC with @CultExciter and friends, got the worst hives I ever had, took a ton of Ativan, got tattooed anyway then went and passed out in the car on the streets of Adams Morgan for a few hours haha.
In short, I would say think about medicating your stimming, even with something like a little benedryl. Make sure you go to the best artist you can get to, trust their judgement on your ideas, but get the tattoo you want. Explain your condition simply at the consult, and most importantly have a good time and don't panic- its a big deal to you but its everyday life to the artist, and you will do just fine.
PS. Im not sure how I come off to other people, but I know @CultExciter and have met @ShawnPorter so maybe they could chime in- Ive been told I have dead eyes or look mad all the time lol