Already seen it but can't complain, it's still funny. I've heard it's an OC parody, but you don't have to have seen it, it just seems like a funny gag.
It's when whats-her-face blonde bimbo shoots the guy who's strangling her emo boyfriend at the end of the first season. The music starts playing when she shoots him.
I probably shouldn't know that, but unlike you chumps I actually went looking for the source.