Leslie Mann and Megan Fox go chest-to-chest in ‘This is 40′

It takes a strong marriage to pull off the intimate scene in “This is 40” between actress Megan Fox and Leslie Mann, written and directed by Mann’s husband and collaborator Judd Apatow. Or maybe it’s just the stuff of married men’s fantasies: Wife, mother and boutique owner Debbie (Mann) catches her best saleswoman Desi (Fox) in a lacy hot pink push-up bra and launches into an awkward discussion about the younger woman’s perky breasts. “Are those real?” Debbie asks, to which Desi replies matter-of-factly: “Yeah, I’m just young.” Talk leads to touch – and then more girl-on-girl touch. Well, the “Knocked Up” director never backed away from a sexual sight gag.

“We saw Megan on ‘Saturday Night Live,’” Apatow told Yahoo! Movies, “and we thought, “Oh, this girl’s wickedly hilarious, and she probably won’t get a lot of these opportunities. So, let’s give it to her, and show everyone how funny she is.”

[Related: ‘This Is 40′: Mom and wife Leslie Mann simmers in husband Judd Apatow’s latest]

OK, that was a safe answer from Judd, who wrote the scene. Again: standing behind the camera while your wife touches the breast of one of the sexiest women in Hollywood sounds like something even voyeuristic Alfred Hitchcock wouldn’t have attempted. According to Apatow, “I get so uncomfortable with even partial nudity in movies. I’ll do one or two takes, and feel weird. Megan is a beautiful woman, but she literally changes the temperature of a room when she walks in.”

“Megan just has great boobs,” Mann confessed to Yahoo! Movies. “Better boobs than I’ve ever seen in my life.”

“I feel very protective of younger actresses because it was so hard for me in the business," said Mann, 40, about her 26-year-old co-star, Fox. And she had other feelings, too. “I wanted to get it over [with] as quickly as possible, because I knew it was uncomfortable for her, probably -- or maybe not. But just in that situation I knew there were a lot of dirty boys around having weird, gross fantasies. And so I wanted to get her shirt back on as quickly as possible.”

See this featurette with Megan Fox and Leslie Mann in 'This is 40':

'This is 40' Featurette: Sales Girl Siren