Steve is ethically reluctant but gives in, training himself by watching videos of "Rain Man," "I Am Sam" and "The Best of Chevy Chase." Once he fools everyone and makes it in as Jeffy, though, it doesn't take long for his new friends to figure out he's faking. The frequently wacky Knoxville finds himself playing straight man to Edward Barbanell, a Special Olympian and a scene-stealer as Steve's know-it-all roommate, and actor Jed Rees as the overly affectionate and enthusiastic Glen.

But in a clever twist, these guys help him keep up his ruse because they're so sick of seeing Jimmy win every year. They subject him to the obligatory training montage — clumsy hurdles at 3 a.m., jabs to the stomach, an elaborate squirt-gun fight — but even that's funny because it has such a silly, gleeful vibe. It's also an ideal fit for the high pain tolerance and physical comedy skills Knoxville acquired during his "Jackass" days.

Some moments feel stiff, even a bit preachy, especially toward the end. And a romantic subplot involving a Special Olympics volunteer who's engaged to a duplicitous pretty-boy feels like little more than an excuse to include the pretty blond Katherine Heigl.

But more often than not, you'll find yourself laughing with "The Ringer," not at it, right along with the characters themselves.

"The Ringer" is rated PG-13 for crude and sexual humor, language and some drug references. Running time: 93 minutes.