A male individual who talks or texts your girlfriend in large amounts, usually with increasing levels of annoyance. Usually this person is not worthy of stealing your girlfriend, just annoying the piss out of you. The difference between a cock block and a girlfriend intruder is that most of the time this person is a friend of yours and doesn't have the intention of stealing your girlfriend either, just being excessively annoying.
Josh: Dude. Whats up?
Brandon: Nothing much. Mike's such a girlfriend intruder
Kyle: Lets eat him.