I wouldn't explain myself to a waitress, from "I'm a disabled" point of view.
Nothing at all against wait staff, I've always found it much better to make friends of bartenders and waitresses/waiters. I am usually a good tipper too. Has never not come back to me.
If it really bothered me, I'd have called her over and challenged her to a drink the same way, while saying "hey, my neck is screwed up, can you do better? Show me a better way to drink without a straw."
Make fun of her legs.
Or, you can give people the permission to laugh at you while you sit there. You can turn that stuff around and not have any proplem.