THE RINGER — ** 1/2 — Johnny Knoxville, Brian Cox; rated PG-13 (vulgarity, profanity, brief drugs).

Just the idea behind "The Ringer" is enough to make you cringe.

Johnny Knoxville stars as an average guy who pretends he's mentally challenged in order to rig the Special Olympics. Hunched over to one side and slightly contorted, referring to himself in the third person by the simpleton pseudonym "Jeffy," he insinuates himself among the athletes who truly have physical and intellectual disabilities with the hopes of winning the thousands of dollars he owes.

It could have been painful to watch in its political incorrectness or, conversely, an insufferably feel-good life lesson.

It's surprisingly funny — often laugh-out-loud hilarious — and yes, inspirational, without trying too hard. At least most of the time.

The names behind the movie help explain the balance "The Ringer" has managed to strike. Peter and Bobby Farrelly are two of the producers. Longtime "Family Guy" writer Ricky Blitt is responsible for the script. And Tim Shriver, chairman of the Special Olympics, is the executive producer in a genius move that ensures the characters are depicted with respect and allows the film to avoid any misunderstandings or controversy.

And it's the scenes that showcase actors who live with developmental disabilities — actual Special Olympians, some making their film debuts — that buzz with the most unexpected comic energy. Director Barry W. Blaustein also uses regular actors playing mentally challenged men to zany effect. All of the characters get a chance to goof on themselves and each other in twisted but well-intentioned ways.

Needing $28,000 to pay for a friend's finger-reattachment surgery — the story is so complicated it literally requires a flow chart to explain it at one point in the film — Knoxville's Steve Barker goes to his loser Uncle Gary for help. (The cigar-chomping Brian Cox plays the role with blissfully un-PC elan.)

Having recently seen a story on television about Jimmy Washington (Leonard Flowers), a six-time gold medalist in the Special Olympics, Gary comes up with the idea to have Steve compete against him and beat him in order to reap the benefits of gambling on the games.

Flowers, a 16-year Special Olympics veteran, is totally believable as an arrogant track star who arrives in a limo with his entourage and wears custom-made, metallic-gold running shoes.