Why do people think im stupid?

So I just completed my junior year and I have to say that was the worst year in my high school. I was placed in everyday algerbra because I have a math problem and I have self esteem issues and depression and a lot of kids had though that I was a idiot or retarded like in math class there was this freshman kid who keeped saying I'm slow. I have ASD/aspergers or degorgies syndrome and I have delayed reaction skills and he was telling me a joke in the hallway where he took a fork and go "he dude check this out Fork you!!! Get it?" And I would take like several seconds to respond to his question and go "yeah I get it" and then he says "Dude, your slow!" And I would just get Mad at him for that. He also calls me stupid in other places and he says I'm a idiot as well and he thinks I'm retarded because in my math class he made a comment to another student saying "yeah you don't need to be in this class but he does." And I got offended by what he says. The thing that offended me most was the one where he said "dude, I'm smarter than you!" And I asked why and he said it was because he thought I was slow. My autism makes me really offended to people remarks so I don't know if they are joking or not. I now think I am stupid and I am a hypochondriac about this. I have a severe daydreaming problem and my mind has a hard time getting back to reality and people just think I'm stupid. I have been facepalmed several times in the past year and been told I was stupid. I cause people to flip out one me when I get a problem wrong. I now hate it when people say dude at the beginning of every sentence now and it bothers me. Am I the only one who was treated like this? Sorry for bad spelling was using yahoo answer mobile. I don't want any rude or sarcastic comments.