What’s the big difference between European and American films? Think “big.”

The 1998 French film “Le Diner de Cons (The Dinner of Fools)” was a modest farce about high-rolling Parisian Pierre Brochant (Thierry Lhermitte) trying to take advantage of dorky Francois Pignon (Jacques Villeret), whose odd hobbies make him a prime candidate for ridicule at the weekly banquets hosted by Brochant and his arrogant buddies.

In “Dinner for Schmucks,” screenwriters David Guion and Michael Handelman surround this slender premise with a multitude of extra characters and gimmicks. If “Cons” was a simple petit four, “Schmucks” is a full-fledged Buche de Noel, drowning in chocolate buttercream, smothered in meringue and dusted with half a pound of powdered sugar. It’s half an hour longer than “Cons” and at least eight times busier, although many of the funniest moments in “Schmucks” come from its simplest aspect: the awkwardness of the relationship between the would-be con artist and his eager-to-please mark.

“Schmucks” offers Paul Rudd as a softened-up version of Lhermitte’s callous businessman; while Brochant came across as a sort of friendly bully, Rudd’s Tim Conrad is basically a nice guy aching to impress his brusque boss, Lance Fender (Bruce Greenwood). Executives at the financial firm where Tim works are expected to participate in Lance’s monthly banquets, in which everyone is encouraged to bring along the biggest loser/nutcase they know. In Tim’s case, that would be Barry Speck (Steve Carell), a mild-mannered IRS paper-pusher who devotes his spare time to creating what he calls “mouse-terpieces,” elaborate dioramas featured taxidermied mice in recreations of “American Gothic,” “Whistler’s Mother” and other celebrated artworks.

Although Tim knows he can score crucial points in the corporate world if he manages to persuade Lance that Barry is an award-worthy dunce, he’s all but overwhelmed by Barry’s overbearing personality and his fervent friendship, and by the time dinner is finally served, Tim is pretty much fed up.

“Schmucks” is directed by Jay Roach, whose credits include “Meet the Parents” and “Meet the Fockers.” So it’s not hard to see why he was a perfect choice for this humiliation-driven comedy, in which Tim suffers one embarrassment after another at Barry’s hands. Some of the situations are genuinely funny, while others are more uncomfortable than they are amusing.

Much of the action in “Cons” unfolded in Brochant’s apartment, but “Schmucks” expands the material the same way moviemakers traditionally “open up” a Broadway show for the screen, ratcheting up the action and bouncing from location to location.

“Schmucks” rolls out a surplus of side dishes, including a rather lousy romantic subplot and a tense rivalry between Barry and his haughty supervisor (Zach Galifianakis) that’s only fitfully funny.

Yet all the accessories Guion and Handelman have piled on seem trivial whenever the movie slows down long enough to concentrate on the chemistry between Carell and Rudd. The two stars have a history together (“The 40-Year-Old Virgin,” “Anchorman: The Legend of Ron Burgundy,” etc.) and their styles mesh wonderfully. Although the screenplay never determines whether Barry is a hyperactive idiot or merely a well-meaning but socially inept kook, Carell works diligently to make this often exasperating man as likable as possible.

As he proved before, Rudd has few peers when it comes to striving to keep cool in the midst of chaos, and he demonstrates that gift again here, particularly when he’s confronted by a demented ex-flame (the vivacious Lucy Punch) or a hilariously highfalutin artist, played to scene-stealing perfection by Jemaine Clement.