What is the difference between fun and fan?

Well, honey, the difference between "fun" and "fan" is about as clear as day. "Fun" is when you're enjoying yourself, having a good time, living your best life. "Fan," on the other hand, is short for "fanatic," someone who's obsessed with a particular person, team, or thing. So, in a nutshell, one's about enjoyment, the other's about borderline unhealthy obsession.