Definitely R. Kelly's
Bump N' Grind! Ever since I heard him sing a portion of it on the Twilight dvd commentary, I've been
aching for the rest. ♥
If you're not familiar with the tune:
link Same video, no song, better quality:
link (the "show" starts @ 4:20)
Robert Pattinson -- THRUSTING. Just. Damn.