It has been his bum that has been doing it for me lately, for the most part.
Steven and I were watching TSRTS on DVD the other night (the DVD most certainly NOT remain the same from the VHS but anyway) Every time I saw a shot of Rob from behind, I was hypnotized and even commented, when Steven noticed I wasn't paying as much attention when he tried to explain something... "Ergh, you could bounce a quarter off that ass!" to which Steven gently laughed, and we continued.
The bulge actually became somewhat tiresome although I think I did make a comment on it at some point during the movie.