“Dinner for Schmucks” kills an awful lot of time getting around to its titular dinner. Like the French film (“The Dinner Game”) it is based on, it takes a leisurely gambol up to the party in which arrogant rich twits each brings a dolt to dinner so they can mock them.

But like a four-star dessert at the end of a hit-or-miss four-course meal, the finale is worth the wait.

Paul Rudd stars as Tim, a go-getter at his investment firm, an analyst ready to move up to the top floor, to make the deals and earn the money to pay for his Porsche and prop up his art-dealer girlfriend (Stephanie Szostak).

But Tim’s got to pass a test with the boss (Bruce Greenwood). He needs to recruit a dope — the bigger the dope the better — for the company’s monthly dinner party.

Tim is weighing the moral implications (the girlfriend doesn’t approve) of this when — thump — he hits a dazzling candidate with his car. Barry, played by Steve Carell with a vacant stare and a malignant giggle, was in the street to “save” a dead mouse. He stuffs them, dresses them up and poses them in dioramas.

And lest you think he’s simply certifiable — he’s got a job, as an IRS agent. He was once married. He’s mastered his cell phone. “My password is P-A-S-S-W-O-R-D.” He cannot pick up a social signal for the life of him, mis-remembers song lyrics and butchers the language (“I’m an eternal optometrist!”).

And since Tim believes “everything happens for a reason,” it’s a date. His accident victim will be his guest at dinner.

But Barry shows up a day early and proceeds to wreak havoc. In a day, Tim has lost his girlfriend, had his car and apartment trashed, faces an audit by the IRS and almost lost a career-making deal.

All this, and the dinner hasn’t even been served.

Director Jay Roach (“Austin Powers,” “Meet the Parents”) keeps the tone more naughty than raunchy. He doesn’t fret over the film’s sluggish pacing. The overlong opening credits set us up for a movie that takes its sweet time.

But, my stars and garters — the laughs.

The laughs build and build, and the little character turns by everyone from David Walliams (“Little Britain) as a dorky Swiss millionaire, and Jemaine Clement (“Flight of the Conchords”) as a pretentious, dim and oversexed artiste to Octavia Spencer as a psychic who talks to dead pets and the lobsters who are the main course at dinner, are an embarrassment of comic riches.

And as funny at playing the kind-of-innocent/kind-of-obnoxious game as Carell can be, wait until Zach Galifianakis shows up. The breakout star of “The Hangover” is the icing on this dessert cart — a demented believer in his powers of “mind control” whose delusion is fed by Barry, who believes this guy really does control his mind.

“Demented” works for the whole movie, from its performance art stunts to the kinky ex-girlfriend (Lucy Punch, a stitch) and Barry’s twisted little “mouseterpieces.”

The situations are painstakingly set up and downright painful to sit through. Enjoy, or endure the appetizers, because really, the dessert is what this “Dinner” is all about.