because the term is not very studly, it is not meant to be used to impress the girl, but just just to lighten the mood of a sexual encounter and make the sex more lighthearted, casual, or less romantic by adding some dumb comedy to things.
boy: mmmh! blow me!
girl: how long are you going to make me do this?!?!
boy: not much longer babe, its time to shine!
girl: OOOOH, give it all to me! i love tasting your jizz!