Here’s the thing about comedies: Even when the script is freighted with formula, the right actors can keep it afloat, even airborne. That’s where I Love You, Man really lucks out. In a down market for giggles (Miss March? Please!), Paul Rudd and Jason Segel are howlingly funny. They have skills. They can get laughs without the sitcom pimping. It’s a rare gift, staying hilarious and recognizably human. Their presence and ace comic timing kick the movie up a notch.

Director John Hamburg (Along Came Polly), who teamed on the script with Seinfeld writer Larry Levin, hangs the plot on a flimsy premise: A dude with no dude friends needs a dude to be best man at his wedding. Never mind that the needy dude, tightly wound L.A. realtor Peter Klaven (Rudd), has a brother, Robbie (Andy Samberg), who could easily do the job. That would leave no reason to get Peter out on man dates. That’s right, Peter’s fiancée, Zooey (a sparky Rashida Jones) — whose girl network is so in the loop they know precisely the first time Peter went oral on Zooey (“Lock that tongue down, girl”) — encourages the poor schnook to go out and find a best buddy. After several disastrous tries, including a gay close encounter, the search ends with Sydney Fife (Segel). Sydney is Peter’s polar opposite, a likable slob who holes up in a Venice Beach man cave stuffed with porn and video games. Sydney has a comfort level inside his own skin that Peter never dreamed possible. Without ever infringing on Brokeback territory, Sydney is man enough to make Zooey jealous. Complications follow, as if you thought they wouldn’t.

And that’s it. That’s all. It’s the variations that Rudd and Segel spin on this theme that make the movie hugely enjoyable. There’s no one better than Rudd at putting an affable face on awkwardness. Volleying nicknames with Sydney — Dude Von Dudenstein, Totes Magotes — it’s always Peter who drops the ball. Cool is always just out of Peter’s reach, and Rudd makes you feel for him. It’s a passion for Rush (the band puts in a surprise appearance) that bonds Peter and Sydney. They rock out in Sydney’s converted garage. Sydney rips open his shirt in joy. Peter undoes a button. Segel has a ball playing the other side of the inhibited musician he wrote for himself in the underrated Forgetting Sarah Marshall. He also lets you in on the loneliness that’s eating at this free spirit.

Credit Hamburg for letting the supporting cast get in its licks. Jaime Pressly is terrific as Zooey’s BFF. Her battles with Jon Favreau, excellent as her blowhard husband, have genuine comic bite. The scene-stealer is Samberg as Peter’s gay brother, Robbie, the most well-adjusted character in the movie. Their dad (J.K. Simmons) calls Robbie his best friend, leaving Peter to wonder what he’s been missing. Of course, he finds it in Sydney. The movie goes soft in its final stages, but Rudd and Segel keep it real. “Sweet, sweet hangin’,” says Peter of knowing Sydney. The same goes for the movie.