The term men use to blame their own shallowness on women.
A girl makes a new friend who happens to be a guy, and he's really nice all the time and she thinks, wow, I have a really good friend. But it turns out the guy isn't interested in friendship, all he wants is to "get some".
Oftentimes, when the guy realizes that he's not going to "score" (how long that takes can vary), he suddenly drops his feigned friendship and moves on to other targets. The girl is left wondering what she did wrong to make such a good friendship fall apart, but of course what really happened was was that the girl had made the mistake of seeing the guy as a real person worthy of her friendship while the guy had only ever seen her as an object.
The guy justifies his behavior by getting together with his buddies and whining about being put in the "friend zone" so that he gets to feel like he's the victim.