I wasn't annoyed but felt compassion and embarrassment for the character. What you observed is a phenomenon known as premature ejaculation. It has happened to nearly every man on the planet and is extremely embarrassing. It can happen to any man at any age but is more likely to happen to inexperienced, young men.
This may seem like nitpicking, but Jensen was playing a character named Jake Gray and the experience happened to Jake, not Jensen.
actually i think it's just movie sex. they were having a quikie. it meant nothing to either one, especially her, so there was no reason for a drawn out experience. sex is always conveniently short in the movies so they can make it more appropriate. if we watched them have sex for 20 minutes it wouldn't be a movie anymore it would be porn.