Obsessive Male Gender Disorder: a disorder that makes one boy crazy. He or she loves thinking about boys, looking at boys, being around boys, going on dates with boys, etc.
This was defined on Season 3 Episode 1 of Zoey 101. Nicole was taken out of PCA for having this disorder by her parents.
However,
the real reason Nicole left the show was because she was involved in many off-screen fights with Jamie Lynn Spears,
otherwise known as Zoey. This caused her to be fired from the show, and her character to be written out.