I always wear Pittsburgh t-shirts.
I was on my honeymoon last week in Jamaica wearing a "Got Ben?" shirt around the resort my wife and I were staying at. (I'm such an obnoxious Pittsburgh fan. It's disgusting.) A bartender there looked at me, read the shirt aloud and said, "Who is Ben?" I went on to tell him who he was, the team he played for, and the multiple championships he's won over his career.
The bartender still didn't really get it -- I don't know how he would if he wasn't a football fan -- but he did hand me a Red Stripe.