I get it often and it's a total shame as I am a 'new' city fan because I didn't actually watch/enjoy football until I was older and my friend forced me to watch his team, man city, play and I became to understand, appreciate and enjoy the sport. He then took me along to wigan away and I was truely hooked. At the same time I started to actually play football (I was the fat kid who avoided sports like the plague but I'll kick your arse on Call of Duty).
So everytime I hear that question I have to admit only since 2008 have I supported city, but it's also the only team I've ever supported.