Some people say wewe can only be an otaku if wewe are able to name at least twenty anime/manga off the juu of wewe head, well i'm sure most of the otakus I know could name only 10 without cheating/repeating. Anyway these are my juu twenty I would name:

1: Naruto
2: One Piece
3: Bleach
4: Inyuasha
5: Hetalia
6:Black Butler
7: Pandora Hearts
8: Soul Eater
9: Fruits Basket
10: Fairy Tail
11: Dragon Crisis
12: Full Metal Alchemist
13. Slam Dunk
14. Prince of Tennis
15. D Gray Man
16. Sword Art Online
17. Highschool of the Dead
18. Amnesia
19. Death Note
20. Angel Beats