People don't understand that even if they are joking, sometimes saying things like "You are autistic" can get into a person's head. Just try to ignore it the best you can, because either way continuing the conversation about it is just feeding the troll. Your brother may have autism, but don't let some idiotic troll get to your head and insult you. The best thing to do in that situation is not let him know that you have any offense. They are bound to lose interest and troll elsewhere. While what he did was terrible, a little internet 101 will say that you made the mistake when you said your brother has autism and that you take offense. A troll will take to offense like a shark to blood.
