In the remake of 'Psycho' (which was actually pretty bad), Gus Van Sant - the director - had Vince Vaughn, as Norman Bates, jerk off while watching Marion (Anmne Heche) get undressed before her shower... he watches her through the hole in the wall behind the painting. It's pretty fast and you don't see his cock, but you hear him breathing heavy and gasp when he cums.