A mere acquaintance who treats you as if you are their best friend every chance they get. A superfan is the person you hate running into in public, because it is usually accompanied by an overly enthusiastic greeting and plenty of forced banter.
1.) I ran into my superfan, Phillip, at the movies last night. I was hoping he wouldn't see me, but he spotted me in the middle of the movie and started shouting my name across the theater.
2.) Colton superfanned me while I was at dinner yesterday. He sat himself down without an invitation and spent 20 minutes monopolizing the table's conversation to reminisce about a class we had together 3 years ago.