A fake fan. Wannabes who want to fit in with whatever's considered popular or hyped in order to gain attention and acceptance. They like something based on the majority of people's interests, not their own. Once that sports team or trend is no longer popular, they will follow whatever is currently considered "cool" or "popular".
bandwagoner: LAKERS ARE A JOKE! LETS GO HEAT!
Dan: Dude.. weren't you a Lakers fan just a few days ago?