Casting affable comedic talents Owen Wilson (2004's "Starsky & Hutch") and Vince Vaughn (2004's "Dodgeball: A True Underdog Story") in a high-concept comedy—and a no-frills R-rated one, at that—would seem at first glance to be a cinematic blessing. Actors, however, can only be funny if they have solid material to support them, and that is a characteristic "Wedding Crashers" is fatally low on. This is an increasingly imbecilic motion picture that starts off with a speckling of laughs before falling apart completely before the viewer's eyes. The brunt of the blame needs to go to screenwriters Steve Faber and Bob Fisher, who apparently never met a hoary cliche or horrid caricature they didn't like.

Thirtysomething divorce mediators John Beckwith (Owen Wilson) and Jeremy Klein (Vince Vaughn) are best friends and lifelong swinging singles whose seduction of choice is to meet the opposite sex by crashing strangers' weddings, sleeping with them, and then promptly disposing of them. At their ages, however, their ritual of meaningless sex has started to finally wear thin for John, all the more made clear when he ends up falling for the beautiful Claire Cleary (Rachel McAdams), middle daughter of U.S. Treasury Secretary William Cleary (Christopher Walken), at her older sister's wedding. Jeremy, meanwhile, quickly beds during the reception the youngest Cleary daughter, Gloria (Isla Fisher), an alleged virgin with hints of nymphomania. Claiming to be distant relatives of the groom's family, John and Jeremy get on Secretary Cleary's good side and find themselves invited to their country home for the weekend. As Jeremy attempts to escape Gloria's clutches, John hopes to convince Claire that he is more suited for her than her current insensitive boyfriend, Sack (Bradley Cooper). Where can their relationship go, though, when his whole identity is based on a lie?

At the onset, "Wedding Crashers" shows some sparks of inspiration, as players John and Jeremy are developed in a breathless whirlwind montage just what their game of crashing weddings is all about, and interest carries over, for a little while, as John and Claire meet-cute in some awfully cute ways. The well wishes don't last long once the setting has transferred to the Cleary's idyllic country home. The family, by and large, turn out to be borderline-psychopaths, with a hatred-spewing, gun-toting homophobic grandmother (Ellen Albertini Dow, the adorable rapping granny in the similar, infinitely superior 1998 nuptials comedy, "The Wedding Singer"); a freaky, over-the-top gay brother, Todd (Keir O'Donnell); youngest sister Gloria, who has one too many screws loose; and a mother, Kathleen (Jane Seymour), who announces she has cheated on her husband for all but two years of their 30-year marriage and wants nothing more than for John to feel her breasts. A little of these annoying characters go a long way, and the utter exaggeration with which they have been written proves to be a huge mistake; because they are onscreen throughout, and because no attempt is made in developing them as people who might live on planet earth, they become as insufferable as a gang of gnats.

At the center of the madness is Claire, a comparatively healthy and normal young woman who would also be classified as intelligent if she wasn't written to be such a slow-witted fool. Much of the conflict built into her budding romance with John hinges on her simultaneous feelings for her boyfriend of three and a half years, Sack. What is so wrong with this equation is that in no way, shape or form is a reason given for why she would be with such a smug, smarmy lout in the first place. He mistreats her right from the get-go, and yet Claire is written to be oblivious to the fact just so there can be some would-be dramatic tension. Despite all this, there is never any question that Claire is going to choose the nice liar over the mean prick, making the drawn-out plot complications all the more lugubrious.

It's a shame, too, because Rachel McAdams (2004's "The Notebook") is like a constant ray of light faced with a giant puddle of muck surrounding her. As Claire, McAdams is so radiant, so likable, and so natural that she could well become the next Julia Roberts, no small feat for an actress who is forced to act like an idiot half the time by a screenplay that keeps her from saying and doing the logical things that could solve all of her problems in a matter of minutes. As crashers John and Jeremy, the typically very good Owen Wilson and Vince Vaughn don't have the luxury of saving their respective characters with bright performances. They try—they really do—but there is something off about them this time around. Wilson gets the romantic lead, but he's unusually bland, while Vaughn's role calls for him to not do much more but either blabber at the mouth for long monologues in a desperate attempt for laughs, or to be put in precarious sexual situations with Gloria and, later, gay Cleary brother Todd.

The rest of the performances are thankless because their characters are so tasteless and one-dimensional, with Isla Fisher (2002's "Scooby-Doo") energetic but exasperating as Gloria; Jane Seymour (TV's "Dr. Quinn, Medicine Woman") used in demeaning ways as the oversexed Kathleen, only to have her subplot forgotten about almost as soon as it starts; and Bradley Cooper (2001's "Wet, Hot American Summer") snarling his face in intentionally spiteful ways as Claire's boyfriend, Sack. Finally, you know you've got a dog on your hands when Will Ferrell (2005's "Bewitched") turns in an extended cameo as a funeral crasher and doesn't get a single laugh.

With "Wedding Crashers," director David Dobkin (2003's "Shanghai Knights") displays no sense of rhythm as he careens from one ill-fated jokey setpiece, and one faux-sentimental bomb of a scene, after the next. Furthermore, the terribly set up climactic confrontation between John and Claire, meant to be the dramatic centerpiece that pulls at the viewer's heartstrings, is ruined to an unthinkable degree by playing itself out in the middle of another couple's nuptials and in front of the rest of the wedding guests. The ways in which director Dobkin treats his audience and his characters like moronic lunkheads time after time is unforgivable, and this finale, like the rest of "Wedding Crashers," rings so falsely that the only ultimate reaction to be had from the viewer is marked disdain. That it isn't very funny or entertaining besides is just the final nail in the coffin of a motion picture headed straight for divorce court.