Then you all understand perfectly, since you've had those assumptions made of you.

Similar history with the tonsils. Plus I had large, severely protruding front teeth from the time my permanent teeth grew in until I got braces when I was a teenager. It was enough to make me have trouble chewing with my mouth closed. For some reason, buck teeth tend to not make a person look very bright. Think of the usual stereotype of an ignorant, uncouth redneck. If their teeth aren't broken off or missing altogether, they're at least sticking out.

On top of this, being sheltered, overcontrolled, and constantly moving from one place to another, I was seriously undersocialized. I also had funny-looking clothes and choppy home haircuts because my family was poor, and my parents weren't willing to spend money on my appearance. They didn't think it mattered that much. If it mattered to me, I'd be told that looks aren't important, and it's what's inside that counts.

I suppose people came to the conclusion that I just didn't have much upstairs, and treated me accordingly. Other kids used to make fun of me by sticking their front teeth out when they talked to me. I did very well on school assignments and tested with a high IQ, but I was told this was only "book learning" and doesn't matter. The social skills I wasn't good with were more important, so you see, I'm not smart where it really "counts." (On the other hand, let me not be real quick to pick up on some skill, and I don't get, "Try again. You can do it." Instead, I get, "See? Not so smart after all, are you? Everybody else can do that easily, but you're just dumb.")

I guess over the years, people just had preconceived notions about me. Before they even got to know me, they'd assume I was dim and treat me accordingly. Every one of the items in the OP have happened to me frequently, and some continue to happen. Which of course makes my social skills even more awkward, because who wants to go out around people who consider you stupid?