Girlfriend in law
When one of your friends starts dating a girl and she all the sudden becomes totally cool with you/conversates with you.
On the scope of available females she just became about as useful to you as your sister. Unless you want to fuck your sister. But if your the kind of person who wants to fuck your sister you probably would fuck your friends girl too.

Anyways this shouldn't become confused with homie hoppers. A girl can only be one of these at a time. Most homie hoppers start as a girlfriend in law but can transform into a homie hopper. But they can NEVER be both at the same time...JH
Girl: Hey how are you?
Me: Bitch I don't cerrr'. I dont wanna be your buddy just cause you fuckin my friend. Quit trying to waste ma damn time ho.
Girl: okay see ya around tee hee (starts skipping away) tralala lala lala

Bitch faced Mitch: Yo, you hittin that?
Me: Nah my homeboy is. She's just my girlfriend in law.
Bitch faced Mitch: word, well that sucks