Interesting question. Harry Potter unlike many other things you might like (Doctor Who, Glee or Lost for example) seems to transcend popularity at most high schools today. Everybody has heard of it and most people love it. Obviously you might not find people who will go to wrock shows with you at your school, but you can still find people who might appreciate a HP reference every once in awhile. If your friends aren't obsessed that's okay though, they're obviously your friends for a reason so you should embrace your similarities as much as possible and maybe save the HP obsession for online. At my college for example everyone likes HP so I mention it sometimes but I've discovered it's not actually the most important thing about me so I can still enjoy my friendships with non-fans. Hope that makes sense!