Sure. Does it make sense for an individual to think about the probability that they (themselves) are a Manchester United fan?
I say it doesn't, really. If you (a) like ManU in some sense, and (b) are willing to call yourself a ManU fan, you are a ManU fan.
Well, in some sense, obviously, you can identify as whatever you please. But it's a rare identity that carries no implications about the world or at least how you react to it. To run with the example, I expect there are a number of imperfectly correlated reasons you might call yourself a Manchester United fan: you might for example feel more excited -- a physical, measurable response -- when watching ManU games than games ManU isn't involved in, or you might be involved with the club's fan community. Generally, however, these are going to be statements ...
Rationality quotes time!
The usual rules: