I am low-spectrun autistic, which is quite common among professional engineers. We do tend to be parodied on TV shows such as the IT crowd (which is rather scarily accurate in many ways!), but as part of a 'stigmatised group' I'd say that being a drunken Scotsman is a more obvious group for me! :-)
I thought at first that I may belong to a stigmatized group, but after much thought I do not believe it is quite the same as what you have faced. Both 'groups' I was considering are very much of my own choosing and from my own actions. I am a little over weight, not sever or anything like that, but in school I was picked on for it - not so much in my adult life.
The second group would be dealing with my support for decriminalizing marijuana, and some misunderstandings about that would be having certain other people dismiss me as another "brain dead hippie pot head" etc....
But As I said before, these are my own choices - so it may not even qualify for the answers you were seeking. And if it does qualify, it is not that significant in the big picture.
I'm a muslim so i've been called terrorist enough times that now i can joke about it, i've had people tell me before that they can't be my friend because i'm muslim too, but what can i say that's life 8)