I haven't seen the episode, but I'm guessing that guy was probably supposed to be some sort of mathematical savant, with great skill in mathematics and very little skill elsewhere.
NTs have grown up with the image of "low-functioning" autistics, not people with Asperger's. They think autism means you spend all day rocking back and forth and flapping your hands, or counting toothpicks, or spinning and pacing. They also think that it means you cannot speak, feed yourself, or control your bodily functions. There certainly ARE autistic people who fit this picture, and because it seems so mysterious and strange to NTs, they find it fascinating. They are especially fascinated by the idea of savants, and some of them think that being autistic MEANS you are savant. They get these ideas from TV and the movies.
Unfortunately, few people are as aware of Asperger's syndrome, which is what most of us here have. They don't realize that having autistic traits does not always mean you are ret*d.
Try thinking of autism as a spectrum, where we all fall at different points. At one end are people with low intelligence who require 24 hour care and cannot function normally in society. These people are usually just called "autistic" or "low-functioning autistic". At the other end are people with high intelligence and abilities who are usually said to have Asperger's syndrome or to be "high-functioning autistic". And of course there are people in between: there are people with medium levels of everything, people with high intelligence who still have difficulty caring for themselves, and people with low intelligence who are still able to learn some self-care.
It can be frustrating to have your abilities underestimated. It does help, though, if you try and remember that being mentally ret*d and being a "sped" aren't always the same thing. Plenty of people with normal intelligence need to be in special classes: people who are blind or deaf, people with severe physical problems, etc. Sometimes people who have Asperger's need to be in such a class too, because a normal classroom goes at the wrong pace for them or causes them too much stress, or because the regular education teacher simply has no idea how to handle their problems. So people may see autistic students in special classes, and assume they are mentally ret*d. They also assume this about blind, deaf, and physically disabled people too. It's a problem most people who are different have to deal with.
And of course some people, like yourself, don't need any special accommodations. If people seem to talk "slow" to you or make fun of you, it's because they don't understand what it means to have AS. They don't realize you can be just as smart as them or even much smarter than they are.
I don't think "sped" or "psycho" are words that should be applied to anyone. I'm not sure how old you are, but a lot of kids and teenagers aren't very nice to people who they see as different. And sadly, many teachers aren't educated on things like Asperger's syndrome, so they may treat you unfairly even if they think they are being helpful.