Yeah,unfortunately,people are always going to stereotype other people,no matter what.Or assume stuff about you that may not even be correct based off of stuff that really doesn't make you who you are,as in the case where people assume you're 'emo',when you'd probably be way happier watching a Harry Potter movie as opposed to watching some emo band.I'm the same way;even though I may have stretched ears,piercings,& tattoos,the stuff I like is alot different than people may assume.
But as far as what your family & friends think,alot of times,when you're young,people assume that when you like something,especially like stretching your ears,that it's just a 'phase'.So they'd likely think the same whether you had autism or not.Or,they just assume you're doing it because of certain reasons,when you're not.I know I had my ears stretched as a teenager,& took them out & let them shrink-I'd listened to everyone else & assumed I'd be happy when I was older,but I missed them too much for many years,so finally did it again at the age of 30.My ears are 1/2" now,& weren't nearly that size when I was younger,but at least I wouldn't have had to start all over again from scratch had I just kept them in.But people are always going to assume that it's just a passing thing that you'll regret when your older.They'll eventually realize that it's not,but in the meantime,if it's something you really love,then you should do it.