An acute condition in which a straight girl turns lesbian. This condition can last from several days to several years but will resolve spontaneously on its own; no intervention required.
"Did Mary really leave Jane for a man? Weren't they together for almost 10 years?"
"Ya, turns out Mary just had a really long case of lesbianitis."
Lesbianitis refers to a girl who has dated men for all of her life but then suddenly decides she wants a girlfriend. Even after obtaining a girlfriend, when she sees hot guys on tv, she declares how much she would like to sleep with them and how hot they are. She never makes comments about how girls look, except to point out the "ugly" ones. Also, you can't call this girl a lesbian or bisexual because she gets upset and throws a fit over it. Lesbianitis, in its most basic form, is pretending to be gay when you aren't.
Nicole must have lesbianitis since she's dating Lisa but hates to be called a lesbian.