Whether extolling the virtues of Sex Panther cologne in “Anchorman,” playing a spirited round of You Know How I Know You’re Gay? in “The 40-Year-Old Virgin” or just ranting about the inane nomenclature surrounding coffee in “Role Models,” Paul Rudd is cinematic comedy’s current king of smart smarm.

He’s long been very, very funny, but never better than he is in “I Love You, Man,” a “bromantic” comedy co-starring Jason Segel (“Forgetting Sarah Marshall”).

There’s nothing special about its plot. In fact, it’s kind of ridiculous and stupid — the kind of thing that exists only in the movies. However, the cast pulls it off with hysterical aplomb.

Rudd plays Peter Klaven, a pretty-much-perfect guy to girlfriend Zooey (Rashida Jones, TV’s “The Office”) and rising real estate star, currently trying to unload the home of Lou Ferrigno, TV’s “The Incredible Hulk,” with open houses featuring deliciously put-together plates of paninis.

When he proposes to Zooey in the opening scene, there’s no reason for her not to accept, and she doesn’t. Only when the newly engaged couple shares the news with the Klaven clan is a break spotted in its foundation: Peter has no male friends, and thus, no one to ask to be his best man.

With support from his wife-to-be, advice from his gay brother (Andy Samberg, TV’s “Saturday Night Live”) and setups from his mom (Jane Curtin, TV’s “3rd Rock from the Sun”), Peter embarks on a series of “man dates” to find the perfect BFF. He succeeds only in finding a guy who gets the entirely wrong idea, and is about to give up when he has a chance meeting with a freeloading but easygoing young investor named Sydney Fife (Segel).

Despite their obvious differences — Sydney is laid-back in every way that Peter is buttoned-up — the two hit it off. In fact, as Peter hopefully tells Zooey, he might be The One.

Inevitably, as formula demands, this pairing can’t help but eventually leave Zooey feeling like the third wheel. The more progress Peter makes in winning Sydney’s friendship, the less time he has for his better half. You can guess how events advance from there.

Originality? Not “I Love You, Man”’s strong suit. Matters? Nah — because the screenplay by Larry Levin and director John Hamburg (“Along Came Polly”) and Larry Levin is awfully funny. Or at least it was funny enough to serve as a springboard for Rudd, Segel and company to engage in improvisational riffing, as one suspects they did readily.

As in “Forgetting Sarah Marshall” and, well, everything he’s ever been in, Segel wears the lovable schlub bit well. His Sydney may be a slacker who spends a great deal of time in his stand-alone garage, sitting in his “masturbation chair,” but he brings out the buried best of Peter, who’s too tightly wound to be much fun.

And that allows Rudd to really shine bright. Peter is uncomfortable letting loose, hanging out with guys, and it shows like a kid forced to wear a blazer to Sunday school. His uneasiness is palpable, and nowhere is it more evident — or hilarious — than in Peter’s attempts to speak like guys do.

After a night of too many drinks and just as many tacos, his off-the-cuff attempt at giving Sydney a nickname stumbles with a leaden “Jobin.” When they make plans to jam together to their mutually favorite band, Rush, Peter replies, “Oh, totally. Totes magotes.” And just wait until he attempts to affect a James Bond accent while trying on wedding tuxedos. Watching someone squirm in awkwardness hasn’t been anywhere near as amusing in recent memory.

It’s Rudd’s most focused persona yet, and he emerges as a viable leading man. He makes every movie he’s in better, but I’d hate to see him revert to the glossy stinkers of his past — namely, anything that requires him to playing a love interest in some TV ingénue’s stab at a big-screen conversion: “The Object of My Affection” with Jennifer Aniston to, more recently and putridly, “Over Her Dead Body” with Eva Longoria. Those smack of feed-the-baby paycheck gigs, but if his trend of guy comedies with heart continues to flourish, hopefully there will less of them to sully his résumé.

No slight to the more outlandish Segel, but “I Love You, Man” is a rare case where the straight man is the funny man. Totally. Totes magotes. —Rod Lott

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