People really can be nasty. Just say what it is confidently, and make yourself sound smarter than they do. If they see that it doesn't phase you and especially if you turn the tables on them and make them feel like the oddball, they'll (hopefully) stop bothering you.
I know it's hard (I'm 16 with a hemangioma, still), but honestly, they don't matter. If they can't accept it, it's their problem. You can be a wonderful person without their approval!
I'm sorry that there isn't much I can do. Good luck dealing with the nasty highschool kids!