With "Dumb and Dumberer," they invented a peculiar new genre — the gross-out romance — and quickly turned it into a blueprint. In the first act, some horrible schlub pines after a beautiful woman. In the third act, he wins her love, when she realizes his innate sensitivity and charm.

Oh, and in the second act, there are a lot of bathroom jokes.

It's not an easy formula to master (although they got it right, once, in "There's Something About Mary"). That hasn't stopped the Farrellys from trying again and again — "Stuck on You" was their latest — or other directors from copying them.

"Along Came Polly" — and if the title makes you remember "There's Something About Mary," some studio marketer will be very happy — is the latest. Heralded as coming "from the co-writer of 'Meet the Parents,"' it's the story of a nervous actuary and a free-spirited waitress. Can they find common ground and true love?

Faster than you can find an exit sign, probably.

Filmmaker John Hamburg's first effort, "Safe Men," was an unfunny Hope & Crosby pastiche, and this movie shows the same clumsy borrowing. The initial set-up — with Ben Stiller cuckolded on his honeymoon — is a gender-switched steal from "The Heartbreak Kid." The central situation — with Stiller falling for daffy waitress Jennifer Aniston — is an opposites-attract cliche you can trace back to "Barefoot in the Park."

As for the final edge-of-your-seat climax — will Stiller realize that Aniston is the love of his life and catch her before she flies away? — its origins are lost in antiquity.

There are some fresh things in "Along Came Polly." Freshest is Hamburg's taste for casting actors in unusual roles. Hank Azaria plays a French scuba instructor. The ever-game Alec Baldwin shows up for a riotous turn as Stiller's crude boss. Philip Seymour Hoffman, of all people — was Jack Black busy? — has a ball playing Stiller's best friend, a corpulent loser still coasting on the one film he made as a teenager.

Stiller and Aniston, though, seem to be stuck playing characters we've seen them do before. Isn't Aniston's ditsy, adorable Polly just a Lower East Side version of Rachel from "Friends"? And didn't Stiller do all this caught-in-a-strange-bathroom embarrassment at least twice before, in both "There's Something About Mary" and "Meet the Parents"?

By the time he's locked in Aniston's bathroom — and Hamburg is dubbing in some explosive flatulence — you can sense the desperation.

You can sense the lack of imagination too. In less than an hour and a half, the movie features several scenes of people in toilets, a slow-motion close-up of Stiller rubbing his face across a sweaty man's hairy chest, a lot of irritable-bowel jokes, a couple of sex scenes, Stiller's naked rear, Azaria's naked rear, an "anal leakage" punchline and an ejaculation gag.

The problem isn't their crudity. "Bad Santa" was crude, too. The problem is that they're not very funny.

It's also a little troublesome that this is what passes for PG-13 these days. And it's truly offensive that a trailer containing the worst of these jokes is currently running before the PG-rated "Cheaper by the Dozen," forcing parents to either take their children hastily back to the popcorn counter or explain why that fat man is telling the skinny man he should spank his girlfriend during sex.

The only bright spot is that if you have seen that trailer, then there's no reason to see "Along Came Polly," which adds nothing to those jokes but time. Besides, you've already seen most of them before in other, better movies. And thanks to the success of the Farrelly brothers' films — and the Weitz brothers' "American Pie" series — you'll probably see all of them many times again.