My son is autistic, "high functioning" and can be bloody rude with it.
He isn't allowed to get away with it. If he refused to be in the room with someone, he is welcome to stay in his room. But never would that person be expected to leave the lounge/kitchen etc just because he didn't want them there.
He gets like this with my MIL, who still treats him like a little child and he can't stand it. When she starts on at him like that, he will often tell her to go home, at which point I step in and tell him that if he doesn't want to talk/play with Grandma, then that is his right, but he doesn't get to tell her to go home, and he can go to his room or be nice. He usually goes to his room (although I'd love to tell MIL to fuck off and stop treating him like a baby!) which is sad, but that's his choice.
No way would he be allowed to refuse to be part of the family at Christmas either. He either joins in with everyone, or he removes himself. I never force him to take part, but it's always him who has to remove himself, never anyone else - it is his choice/desire after all. And to be fair, he will often get a grip on himself and join in, or at least stay in the room.
If your brother doesn't want you around, then he needs to remove himself. He doesn't get to dictate what you do. If you want to go into the lounge, then go. If you want to open your Christmas presents in the morning then do it. Your parents need to step up and tell him that he doesn't get to dictate to everyone else what they do.
Autism, as others have said, is not an excuse to be a prick. It sometimes needs other ways to make things work, and it's not always exactly what others want, but it is not a reason to bow down to someone else's wants, which are no greater or lesser than yours.
Your parents are mostly at fault here though, they really should have put a stop to this early on, not laughed and made it a joke and expected you to remove yourself from the family. This is why people go NC later on and the parents have no idea why.