My mate's such a hipster, even when it comes to racism. He claims he hated Muslims way before 9/11.
I don't think that is a very appropriate thing to say. Why do you think racism is something to joke about? Are you racist?
It was a joke. Learn to take jokes. No, I'm not racist.
Though you are joking, the joke is still predicated on the belief that all Muslims are terrorists and that line of thinking is wrong since it spreads hate against Muslims. This could lead to people acting out on their hate and assaulting Muslims in public. Instead of joking about Muslims it would be better and more appropriate to find other subjects to joke about.