-That I am smart because I read a lot.
p-ull-ease…
When people say that to me, I go out of my way to explain that reading is no different than watching television. It’s all input, and unless it’s textbooks, I’m not learning a damn thing. (Not true, actually, but I’m not learning much factual; I’m just enjoying the weather in there. )
I think the funniest was the game after the first hockey game my husband went to. I’ve been a season ticket holder for years, he rarely goes. He’s tall, slim, clean cut…and the game after I must have had a dozen people ask if that was my husband and say “He’s not at all the kind of guy I pictured you being married to.” When I asked what kind of guy they had pictured, they all said “Oh, some kind of biker dude”.
And since I never wear shorts to games most of them didn’t even know I have extensive tattoos!
Are you generally in the pub during these assumptions? 
As for me, everyone assumes I’m vegetarian. I’ve been warned in midreach for food at buffet’s “that’s got chicken in it!!” Umm, yes, that’s why I want it. I could kind of understand it back when I had waist length dyed hair and wore doc martens a lot, but I’m a lot more mainstream appearing nowadays, and still get it.
Because I’m a big, kind of scruffy-looking guy, that I’m (a) stupid, (b) tough, © like loud rock music, (d) smoke, and (e) play football.
Because I can write coherent sentences and generally speak in a fairly soft, moderated voice that I’m a wussy, effete intellectual type.
Because I enjoy science and science fiction (and particularly STAR TREK) that I’m a nerd.
Because I started learning Russian in high school that I’m a Communist.
Because I’m fascinated by the Hitler Era and World War II that I’m a Nazi.
Because I don’t buy most of the rubbish taught in American schools about the Civil War that I’m pro slavery.
Because I was lucky enough to receive a good education that I MUST be a liberal Democrat!
Because I think most liberals are full of crap that I MUST be a retarded, blindly obedient Republican.