Standup Bass
When your girlfriend is on top with her back against your chest and your penis in her anus while fingering her clitoris and stimulating her nipple.
Boy 1: "Yeah dude I was playing the Standup Bass"
Boy 2: "Isn't that where you fuck her in the ass while stimulating her clit and nipple?"
Boy 1: "Yeah dude"
Boy 2: "Isn't that where you fuck her in the ass while stimulating her clit and nipple?"
Boy 1: "Yeah dude"