To me it's very simple a real fan is someone who is sticking with his team through thick and thin, the good and the bad times. The problem is, some people are confusing the term real fan with fanboy but they aren't the same. A fanboy will go out of his ways both verbally to defend every move his chosen does make or doesn't make while a real fan will look at things more rationally and also criticize some moves if he feels it's justified.
So basically a real fan is the opposite of a bandwagoner.
I think most people here who complain do stick with the team through think and thin. Otherwise, they'd stop posting, because they'd have stopped watching this mediocre team by now. The fact that they post means they still watch and care.
Then again, the two greatest philosophers in history were both pessimists, so I'm all for it.