That was a dirty trick. Get a movie with some actual boobs. He's PG-13 and R level now. Guys like tits. That's that. It isn't like he can't get them on the Internet. I'm not talking porn movies, but just ones that actually do show some flesh. There are too many to list and I'm sure you've seen enough of them to have something in mind. Let him watch it alone. There's nothing unnatural or wrong with that, but FOX and the Dubya administration don't have boobs - they've got anal cysts.
There's nothing wrong with tits. Tits are natural. They're fun to play with. They're also food. Guys like tits. Originally it probably developed from a view that big tits produced more milk, which is not true by the way. But it is instinctive for guys to want to see tits. As a father of three beautiful and nearly full grown daughters, I can attest that my wife's tits were a major factor in what they became - she breast fed them all, even while in school board meetings (of which she was an elected member). I'm a "more than a handful's a waste" sort of guy, but that is always going to be a point of attraction for guys. Second base, if you will.
The only thing you need to do is point out that while the female form is beautiful and inspires sexual desires, that doesn't make a female any less qualified for any position a man might take. I get on guys' asses all the time about the "women can't do a man's job" bullshit. My wife is a 3rd degree black belt and my three daughters are all second degree black belts. My middle one runs the school's demonstration team. Don't fuck with these chicks!
Oh, and just for a plug, my eldest (junior at McDaniel) is spending this semester in Budapest. Her blog is KrystinasCrossings.com
There's nothing wrong with sex. Kids are going to have it and pornography is why the Internet (and VHS for that matter) exists. Just tell them what I've always said - "PUT A RUBBER ON IT!"