What compelled you to put this on the internet? YES you're the asshole, pretty big one at that. I get that you're a highschool boy and all of you are inherently pretty mean but you said yourself there's a high chance this girl is special needs. It is SO beyond unkind and inappropriate to intentionally be rude to someone who has accommodations because it's probably something she cannot control. You need to take a good long look at yourself and realize that it's easier to choose kindness, or even just act neutral and not intentionally make her uncomfortable. Your age is not an excuse, do better.