By now it's been widely noted that "I Love You, Man" is not a Judd Apatow comedy — although it's like one. The stars, Paul Rudd and Jason Segel, have previously featured in two of Apatow's biggest hits, "Knocked Up" and "Forgetting Sarah Marshall." And while the story — yet another expedition into the dark, cluttered heart of Guyville — isn't as besiegingly gross as some of the master's best work, it's nevertheless rousingly funny at times, and overarchingly sweet, in the Apatow manner. It's also naggingly implausible, though, which may be a minor annoyance even for the movie's designated demographic.

Rudd plays Peter Klaven, a hyper-mild-mannered Los Angeles real-estate agent. If nothing else, Peter is the perfect boyfriend — the kind of guy who, upon coming home to find his fiancée, Zooey (Rashida Jones), in full twitter with her gossipy girlfriends, will slip into the kitchen to whip up a tray of root-beer floats for them. Very cute — and (in the movie's view) kinda gay. For reasons that are not at all clear, Peter has no male friends, no buddies. This has apparently never been a problem until now: With a wedding coming up, he realizes he's going to need a best man.

In his search for a pal, Peter first consults his brother, Robbie (Andy Samberg), who, as it happens, is gay. He also trolls the Internet a bit. The results of these initiatives are predictably disheartening (and pretty amusing). Then, while presiding over an open house one day at a property he's trying to sell, Peter meets Sydney Fife, a guy who is everything that Peter isn't. Sydney makes the rounds of these house-hunter wingdings strictly for the free food and horny divorcées (the only kind of women he's interested in). He's converted the garage behind his house near Venice Beach into a "man cave," filled with guitars and amps and booze, with a special area set aside for what might be called basic male fulfillment. Sydney is big, loose and goofy, a natural hipster. Peter is a stranger to cool, especially of the verbal variety. He actually says things like "See ya in a jiff." But when he tries to improvise — "We're just chill-axin' " — he sounds like even more of a dork. And when he attempts a laid-back Jamaican patois — "Me slappa da bass" — he sounds like a leprechaun.

At first, Zooey is happy that Peter's found a buddy. But as he slips deeper into Sydney's testosteronic world, with its endless bar hangs and Rush-heavy rock soundtrack, she grows worried — the two of them are starting to seem a little ... gay. The movie flirts with an interesting subject: straight-male anxiety about homosexuality. But it's too constrained by its comedic formula to do much in the way of sorting that subject out, and in the end, the modest narrative tension it provides disperses in a cloud of bro-com bonhomie.

Fortunately, there are some very funny scenes — even the inevitable fart-joke interlude is a scream. Rudd doesn't have a chance to really cut loose here — there's nothing as madly freewheeling as the stoned-age surfer he played in "Forgetting Sarah Marshall" — but he anchors the film with his virtuoso social discomfort. There are also some lively bits tucked in around the edges, especially by Jon Favreau as one of the world's most abrasive macho men, and Lou Ferrigno — the original Hulk! — as the celebrity whose house Peter is failing to sell. ("Don't make him angry!" Sydney warns.) But it's Segel who owns the movie. His character is so ambiguous at first that he seems sleazy beyond the call of comedy. But when we see him slouching along Venice Beach with his dog and airily waving away angry neatniks alarmed by the clumps of poop the wee creature is depositing in the sand ... well, here's a guy we might not mind hanging out with ourselves, right? Probably wouldn't want to bring him home, though.

(Paramount Pictures has a piece of "I Love You, Man." Paramount and MTV are both subsidiaries of Viacom.)

Don't miss Kurt Loder's reviews of "Duplicity" and "Knowing," also new in theaters this week.

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