Who's the guy who, late in the movie, jumps from the left side of the frame, grabs Leon's love handles, shakes them, saying "Leon's getting too fat! He's too fat!" and then jumps back out of the frame, leaving Leon astonished and speechless, staring to the left? And who is Leon?

It looks like an ad-libbed scene to me: "Leon" was absolutely struck dumb by the move.