Jack Black Grows A Mustache, Drops Trou For ‘Margot At The Wedding’

'It's a full moon rising,' funnyman says of nude scene in dramatic new film.

BEVERLY HILLS, California — With “Margot at the Wedding” marking his first starring role in a dramatic film, Jack Black has some very weighty issues on his mind these days.

“What was a great mustache?” Black pondered. “Tom Selleck’s is the most famous mustache probably. … Burt Reynolds … it’s kind of a ’70s, early ’80s thing. Maybe I’m bringing the mustache back in this movie.”

The manic movie star is talking about the facial hair of his character Malcolm, an unemployed artist engaged to Jennifer Jason Leigh’s troubled Pauline, in “Wedding.” The newly released film also stars Nicole Kidman as Margot, Pauline’s cynical sister who finds their family’s quirky issues being worked out over one very long weekend. Many of the film’s much-needed laughs, however, come from Malcolm’s need to not only grow a ‘stache, but constantly remind everyone of its tongue-in-cheek nature.

“I like the soul patch,” Black said of his own real-life soup-catcher preferences — “Nacho Libre” mustache notwithstanding. “I’m just letting it grow, Sasquatch-style, right now. I should’ve trimmed it up for this interview. I like to incorporate the patch, though, in whatever facial hair I do.”

But it isn’t the hair on his upper lip that has Black’s fans buzzing these days. During a love scene with Leigh, the “Tenacious D” frontman appears in a doorway nude, leaving behind a revealing shot of his back end.

“I’ve had a lot of ass work,” he said, remembering movies where he’s dropped trou for comedic effect. “But this one was a dramatic ass — and it’s a full moon rising.”

To prepare for the cheeky monologue, Black was careful to keep it real (“It was in the script and you gotta do it, because that’s the way people are in their bedrooms”), and he’s careful to point out that such authenticity didn’t include a quickie course in “Buns of Steel.” “Obviously not,” he laughed. “But I should’ve. Oh man, when I saw the screening of this I was like, ‘Dude, mix in some crunches! Some ass crunches!’ Sit-ups are good for the abs, but what’s good for the back fat? Power squats?

“I needed to do something, but it’s too late now,” he sighed. “Unless, for the DVD release, I’m thinking I might be able to pay for a computer ass-fat reduction. But I don’t know how much that will cost.”

Possibly in an attempt to help finance his CGI slim-down, Jack has front-loaded his acting schedule with more than 10 films in various stages of development — and most will return him to his comedic roots.

“I had a really good time doing ‘Ghostbusters,’ ‘Rush Hour,’ ‘Driving Miss Daisy’ and ‘RoboCop,’ ” he said of the movies he enjoyed re-creating alongside Mos Def for January’s “Be Kind Rewind,” a Michel Gondry flick about video store clerks-turned-filmmakers. “They were all fun.”

These days, the funnyman is busy shuttling back and forth to the Hawaiian set of Ben Stiller’s action-comedy “Tropic Thunder” and keeping a close eye on the writer’s strike . “Hopefully the strike will get resolved,” he explained. “And there will be more to come after that.”

The big Black news, however, is that he hasn’t only joined Harold Ramis’ biblical comedy “Year One” alongside the red-hot Michael Cera and Judd Apatow, but that the group will try to squeeze the film in before the next picketers lift up their signs. ” ‘Year One’ we’re doing before [next summer's] actors’ strike,” he revealed. “It’s already been written, so there’s no more writers. Obviously, no writers can write on it now.”

Although details on the project have been rare, Black was willing to cough up a few tidbits. “[Cera and I] are just two dudes wandering through early civilization, trying to find the meaning of life,” he explained. “It’s kind of like those old Monty Python movies, like ‘The Meaning of Life’ or ‘Life of Brian,’ a funny look at biblical tales.”

Despite earlier reports that the yesteryear comedy would feature Owen Wilson as a slacker caveman, Black revealed that both the plot line and the “Darjeeling Limited” star will be absent to filmgoers. “[Wilson] is a producer,” Black explained. “It’s not prehistoric, it’s just pre-Christ. It’s like an old, biblical tale, Cain and Abel-type stuff. … It’s very funny. Harold Ramis and Michael Cera are very talented, and I’m excited to work with those guys.”

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