Context, from Wikipedia:
"Pumps and a Bump" proved to be a controversial track on [The Funky Headhunter], somewhat affecting Hammer's image. However, the single peaked at #3 on the US Rap charts. It was banned from heavy rotation on MTV with censors claiming that the depiction of Hammer in Speedos (and with what appeared to be an erection) was too graphic.
When I think of an MC Hammer impression, I think of the dance from "U Can't Touch This," but to each his own.