Recently Merriam-Webster added a 100 words to their dictionary. One of these words is "fanboy".
fanboy
Main Entry:
fan·boy Listen to the pronunciation of fanboy
Pronunciation:
\ˈfan-ˌbȯi\
Function:
noun
Date:
1919
: a boy who is an enthusiastic devotee (as of comics or movies)
http://www.merriam-webster.com/dictionary/fanboy
Now what is not listed is Fangirl and according to Merriam-Webster, the word "fangirl" hasn't be citied enough in various well-known and print sources.
Gia Manry over at
http://giapet.net/2008/07/07/fanboy-gets-legitimized-no-luck-for-fangirl/
got a full e-mail from Merriam-Webster explaining how a word gets added to their dictionary.

