If it bothers you, then talk to him about it.
Why are you dating a guy you feel you cannot talk to?
If he says it's hypocritical of you to comment on handsome male actors, then reply with, "OK, I understand. So how about we both agree that we won't comment on other people's appearances in front of each other? Sound fair?"
That being said ... there's a difference, maturity-wise, between an adult (man or woman) watching a movie and saying, "Wow, So-and-So is really attractive" versus "Wow, look at the way So-and-So's breasts jiggle when she runs." Especially an adult in a happy relationship.
If you're dating the kind of guy who's immature enough to talk about another woman's jiggling breasts - right in front of his girlfriend no less - take a look in the mirror and ask yourself if he's really the best you can do.