a girl is on her period

to be all up on someone's girl when hes right there

Trying to take/having an afair with someones girl.

When another guy is trying to holler at a girl you are in the mist of trying to get with

Messing with, trying to steal, or interfering with someone getting a girl.

To engage in intimate relations with someone else's significant other.

A saying used when you want to tell someone who's interested in your girlfriend/boyfriend to back off. Using this saying means not only 'back off' but that the target is your property.