I grew up a fan of the Bengals. It's possible that I still am one.
I'm not positive, though. I mean, I watch the Bengals when I'm near a television and they happen to be playing. When I'm in my car on Sundays in the fall, I listen to the broadcast. This ritual has played itself out hundreds of times over the course of my lifetime, most of which was spent in southwest Ohio, so in theory I want them to win more games than they lose. Which technically makes me a fan.
On the other hand, being a "fan" of something generally requires some kind of emotional attachment to the thing that you're a fan of.