Brandon: OMG! You're a cousin fucker!
Me: I AM NOT! Just because everyone says my cousin is hot and he wants to get in my pants, does NOT mean I fucked him!
Brandon: Nah, you fucked him.
Me: HE WISHES!
Brandon: Yeah OK...cousin fucker.
Me: GRAWR! (eats Brandon)(or not)
It is the name of a song from the Broadway show/movie, RENT. It is used describing the situation of going out with someone who's bisexual, who likes to cheat and flirt with other men and women, and it's very hard to leave them. Because that's what the song's about.