This term comes from the movie "What Lays Beneath" in which two lesbians have sex in the bathroom. One of the women bends over the sink while the other fingers her from behind. She inserts both hands such that they are facing each other, palm to palm, and then she begins a clapping motion. Reminiscent of a toy monkey with symbols, the term monkeyclapping was born.
Holy shit! Last night was crazy. I just monkeyclapped that girl that we met at the frat house.