Disclaimer: Just because you are a fan of said item, doesn't mean you act this way. I am speaking in the most general terms of fans. For example, I am a fan of Harry Potter, Lord of the Rings, Star Wars and Star Trek. But I act like a LOTR fan....mostly.
1. Twilight
2. Harry Potter
3. Lord of the Rings
4. Doctor Who (and Sherlock)
5. Star Wars
6. Star Trek
Honorable Mention: Anime
Yes, there are so many more fandoms on the scale, but I feel like these are the major blips on it.