Straight friends Ben (Mark Duplass, left) and Andrew (Joshua Leonard) decide to make a gay porn movie together in the adult comedy Humpday. (Maple Pictures)Just when the "bromance" seemed on the verge of running out of steam, along comes Humpday, an indie film that both belongs to that ubiquitous man-child genre and invigorates it.

Humpday begins as 30-something marrieds Anna (Alycia Delmore) and Ben (Mark Duplass) are in bed, gearing up for a round of prime-conception-time sex. As they giggle at the realization they're both too tired to even bother, they give off the air of partners who've hunkered down into an easy, comfortable groove. That settled vibe is instantly ruffled when they are wakened by a late-night visit from the scruffy, belly-laughing Andrew (Joshua Leonard), Ben's long-lost boho college roommate who's just returned from some vague artistic endeavor in Mexico.

Humpday delves into interesting new terrain where most other dude-centric comedies have previously feared to tread.

Faster than you can say You, Me and Dupree, Andrew is crashing in the basement of Ben and Anna's tastefully outfitted Seattle home and wreaking havoc in their responsible, adult lives. Anna is a bit horrified at all of the arm-punching and "I love you, mans" that are exchanged, though to her credit, she attempts to bond with the hyperactive house guest, even offering to cook her special pork chops in his honour. But Andrew has other things in mind, namely regression. Soon, the two male buddies are ditching dinner in favour of an aptly named "Dionysus" house party, where they listen to music, do a lot of bong hits and try to recapture some of their faded college-days glory.

Ben, in particular, relishes the chance to revisit his wild former self. When his sexually omnivorous party hosts begin discussing an amateur porn film festival called Humpfest, he's just tipsy enough to chime in with uncharacteristic gusto. In no time, he and Andrew have pitched their own project: they will star in the first-ever straight male porno, where their sex scene will serve as a boundary-shattering artistic statement, pushing the porn genre into a new realm that is "beyond gay."

In the harsh hangover light of morning, as the buddies snack on tablespoons of sugar and head to the driveway to shoot some hoops, a series of anxious, averted-eyes close-ups suggest they both remember their drunken pitch, and are avoiding the moment where they have to discuss what comes next.

It's at this point that Humpday starts to delve into interesting new terrain where most other dude-centric comedies (save for the genuinely touching Superbad) have previously feared to tread. If these guys love each other – and they do – will their guy-on-guy porno debut make them somehow less straight? Worse still, if they back down from the project, will that be like admitting they're not as free-spirited and cool as they once thought they were?

Humpday's two man-children discuss this conundrum endlessly, examining it from every angle, including whether they should even tell Anna about the secret porn pact. The actors' improvised comic exchanges are captured in a DIY, handheld camera style often associated with mumblecore, and like most of the films emerging from that movement, Humpday devotes a lot of time to some very smart chatter about relationships. As Ben and Andrew talk themselves out of and back into bed several times, fresh insights into male behaviour keep cropping up – among them, Humpday's central notion that a guy's sometimes shaky self-image can be deeply rooted in how he's perceived by his dude friends.

Anna (Alycia Delmore, right) learns about husband Ben's unusual film project. (Maple Pictures)The film's director, Lynn Shelton, offers up a liberal view of sexuality in Humpday that I found refreshing after seeing the brash yet adolescent antics in another recent gay-themed film, Bruno. While Ben and Andrew are at a debauched house party, their fellow revellers – including hostess Monica, who has a girlfriend but also requires some occasional "boy time" – all struck me as embodying the "anything goes" spirit the goofy protagonists are striving to achieve in their porn project. In Humpday, any kind of sex is permissible, as long as there are some pretty clear boundaries in place and no one's getting hurt.

In another of the movie's inspired touches, Anna, the character who stands to suffer the most if the boys' project ever achieves liftoff, proves to be far more interesting than her white-picket-fence surface initially suggests. Alycia Delmore's honest, painfully funny reaction shots are worth the price of admission, and she makes Anna a three-dimensional alternative to the nagging shrews and whorish bimbos who've populated most recent bromances.

As the time for Ben and Andrew's close-up fast approaches, and the two anxious buddies lie side by side on a bed, I was reminded of Paul Mazursky's smart comedy, Bob & Carol & Ted & Alice (1969), where the titular characters contemplated taking a similarly taboo-busting leap. Though I can't tell you whether Humpday's buddies decide to boldly go where no bros have gone before, I can reveal that Shelton's movie is as smart, complicated and attuned to her times as Mazursky's est-era romp was to his.

In its own understated way, Humpday does go beyond gay, and it winds up in a far murkier place, where everyone – male, female, straight, gay, bi – is more than a little freaked out at the prospect of navigating relationships in all of their messy glory. Like Mazursky before her, Shelton has made a movie that looks like it's about sex, but ends up feeling a lot closer to a rousing rendition of What the World Needs Now Is Love.

Humpday opens in Toronto, Montreal and Vancouver on July 24.

Lee Ferguson writes about the arts for CBCNews.ca.