Let's get a list going, I'll start
1) Unkempt/Has a neckbeard
2) Owns a fedora
3) Doesn't own a car
4) Height starts with a 5'
5) Unnatural hair colour
6) Asian
7) Watches anime
8) Doesn't exercise/play any sports (or plays sports but isn't very good at it)
9) Doesn't offer to cook for me by third date
10) Owns comic books
11) Watches Doctor Who
12) "I don't like spicy food"
13) Has close friends who are female
14) Plays League of Legends or World of Warcraft
15) Acne
16) Still talks to his ex
17) Doesn't like Game of Thrones