In the lengthy, grim annals of movie awfulness (yes, it's been a long year, can't you tell?), unfunny comedies hold a special place of honor. And, within that category, there's an even more special place for long, unfunny comedies — those movies that contain perhaps one joke at best but keep pounding away on it for the better part of two hours or more. And now, within that category, is a place for Long Unfunny Comedies From the Farrelly Brothers That Nonetheless Feature Puzzling Yet Weirdly Endearing Performances By Meryl Streep and Cher. "Stuck on You," as you can see, is a bit tricky to classify.

Surprisingly, it's not entirely unwatchable, despite the dopey one-joke premise. Matt Damon and Greg Kinnear play conjoined twins Bob and Walt Tenor (Damon's character got most of the liver, we're told, which is why Kinnear's twin looks so much older, ho-ho), owners of a burger joint on Martha's Vineyard. When Walt (Kinnear) gets the acting bug, the two head for Hollywood — which doesn't exactly greet the pair with open arms.

Writer/directors Bobby and Peter Farrelly, whose mega-hit "There's Something About Mary" brought new meaning to the words "hair gel" a few years back, are known as masters of sunny gross-out comedy. While "Stuck on You" is certainly sunny — nearly every character is sweet-natured, and the brothers have an affectionate bond that isn't played for laughs — those eagerly awaiting bodily fluids, or laughs, will be sorely disappointed.

Movie review Showtimes and trailer *½ "Stuck on You," with Matt Damon, Greg Kinnear, Eva Mendes, Seymour Cassel, Cher. Written and directed by Bobby Farrelly and Peter Farrelly. 118 minutes. Rated PG-13 for crude and sexual humor and some language. Several theaters.

The Farrellys throw the occasional slur into the mix, but the "offensive" moments feel half-hearted; it's as if they're putting this stuff in because the audience expects it and moving quickly along. (Students of the Farrelly oeuvre will be pleased to spot, however, a subtle hairdo homage to "Dumb and Dumber": Damon sports Jim Carrey's dorky bangs; Kinnear's hair is reminiscent of Jeff Daniels' blond fluff.)

So there's nothing outrageous whatsoever about "Stuck on You" — until Cher's first appearance, dressed in an outfit seemingly inspired by an Edwardian rock 'n' roll rooster. (Who knew such things existed? Every movie, let us remember, teaches us something.) As an actress, Cher is, ahem, somewhat changed since her "Moonstruck" days; her face no longer moves freely but seems cemented into place. But her performance has a pleasing tone of self-mockery; she's Cher playing "Cher," sabotaging her TV series by casting the hapless Walt.

Racking up even more good-sport points is Streep, gamely playing herself as the object of Walt and Bob's movie-star worship. Also on hand are Seymour Cassel as Walt's old-school agent, with a hair-hat toupee and a blacked-out front tooth that mysteriously appears and disappears, and Eva Mendes' cleavage, displayed in a wide variety of push-up bras, which appears to have a hard-working agent of its own.

Does all this add up to a movie? Nope; nothing much happens in "Stuck on You," a seemingly endless movie strangely devoid of laughs. The Farrellys' earlier movies worked because they ably mixed sweetness with outrageousness; this time it's all sugar. When even Meryl Streep can't save your movie, something is very wrong indeed.

Moira Macdonald: 206-464-2725 or mmacdonald@seattletimes.com