Rear Flank Downdraft
To cum in a girl's ass. Originally a meteorological term, meaning in a supercell thunderstorm, an area of dry air that wraps around the back end of a mesocyclone.
Guy 1: Boy, I sure like that girl Brandi! I'd like to give her a rear flank downdraft.
Guy 2: Ya me too man.
Guy 2: Ya me too man.