A combination of "spotting" and "tea-bagging". I was at the gym watching a guy spotting for another guy who was doing bench presses. The guy who was doing the spotting was standing right over the face of the guy who was doing the bench presses. The term just seems self-evident.
Josh was trying for a new personal record on the bench press, but his spotter, Zack, was in a playful/sick mood. Before Josh's record set was finished, he'd become the victim of a spotbagging.