Done on a dare

Chicken! That’s the real game being played in “Humpday,” the improvised comedy-drama by Lynn Shelton about two old college friends, highly competitive and decidedly straight, who end up daring each other to have sex together on camera. Playing Ben is Mark Duplass, best known as one of the writing and directing Duplass brothers, wheels of the super-low-budget, independent film movement known as mumblecore. Duplass knows about taking seemingly unfilmable ideas (such as the genre mash-up “Baghead”) and making compelling movies.

But “Humpday” was a little different. It “was like, ‘This might not work at all. I’m not interested in turning this into a farce,’ ” he said at the 101 Coffee Shop in Hollywood, acknowledging that the daring premise’s plausibility was the biggest hump.

“How do we get dudes in the theater to say, ‘Oh, my God, I could see how I might get wrapped up in something like this with my over-competitive best friend.’ What we discovered was all we had to do as characters was voice the very concerns the audience might be having. And by calling out the ridiculousness of it all, it really helped -- I don’t know what it is, it just kind of saddles it for the audience a little.”

Ben is riding a comfortable groove with his job and wife when Andrew (Joshua Leonard of “The Blair Witch Project”), his fearless artist buddy, suddenly appears: “It’s that trigger of feeling like that special time in your life when you’re 18 to 22, when the world is completely open to you and everything’s a possibility, and you talk with an idealism that kind of seems stupid, but it’s full of life -- you never do or say so many carpe diem things as you do in college, you know?

“Ben thinks, ‘I’m in danger of becoming a suburban nobody,’ and it scares him. The wolf who is chained will chew off his own foot, so it’s kind of freaking him out a little bit.”

Duplass knew that the loving, envious, admiring one-upmanship required a certain spark from the performers.

“He and Andrew, like Josh and myself, are both really nice guys -- with enormous egos and high-grade tempers,” he says with a laugh that does not negate his sincerity. “So while Josh and I could play these great friends, boiling under the surface would be, ‘I’ll kill you if you say the wrong thing to me.’ ”

But not only were the characters threatening to collide, the actors were racing toward their own walls of inhibition. The film is entirely unscripted, with performers improvising dialogue to fit roughly planned scenarios . . . until that climactic scene in which Ben and Andrew meet in a hotel to go through with their scheme, intended as an art project. That scene didn’t even have a framework.

“I had this idea: What if we shoot the whole movie in sequence and we won’t know anything that happens in the hotel room?” Duplass says. “We didn’t know. Maybe there wouldn’t be any homosexual element; maybe there would be some. That allowed us to be as honest with the previous 80 minutes as possible and not try to land on a certain moment that was false.”

With such subject matter, the film may have a tough time luring viewers who are a bit queasy about the topic. But just as the Chinese character for “crisis” also means “opportunity,” Duplass wonders if the written character for “Brokeback Mountain” might double for “I Love You, Man.”

“Humpday” is “naturally going into certain markets that are more art-house skewed,” he says, rattling off the distribution and box-office statistics that made the Duplass brothers’ acclaimed “The Puffy Chair” rank a success.

“That being said, there is something about this movie that is tapping in a little bit to this -- I guess it’s in the zeitgeist -- this ‘bromance.’ The inexplicable nature of dudes’ attraction to each other and their competitiveness that schlubby guys are able to express on screen right now. Maybe there’s something in that that will tap into the guys who wanted to see ‘I Love You, Man’ or ‘Superbad.’

“This is going further. Obviously.”

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Where you’ve seen him

Mark Duplass is best known as half of the indie filmmaking duo the Duplass brothers, with older brother Jay. Their glowingly received features “The Puffy Chair” (in which Mark starred) and “Baghead” are often associated with the mumblecore movement but are atypically plot-driven for such indies. Their breakthrough is the hilarious, no-frills digital short “This Is John” (available free online), shot in utter desperation in their kitchen after what Mark Duplass describes as “another failed feature.” The actor will soon be seen in Noah Baumbach’s “Greenberg,” as well as “Mars,” a rotoscoped astronaut movie. The brothers’ next film, an as-yet-untitled project for Fox Searchlight, stars John C. Reilly, Marisa Tomei and Jonah Hill.

-- Michael Ordona