The sentence "person who thinks that <product> is the best because it has <feature/characteristic>" returns true for pretty much every human being.

Not everybody is a fanboy though. Just everybody has a preference. Most of us here are gathered because for us <product>=N9xx and <characteristic>=linux. A happy prius owner thinks his car is the best choice because it's hybrid. He's not a fanboy by definition. If he goes up to a ferrari owner and tells him that his car is better because nobody would ever want to go faster than 170mph, and that is illegal to do that anyway, that would make him a fanboy.