Coincidences are essential components in fine comedy—just think of Shakespeare, or Mozart’s “Figaro.” But if you pile too many of them together, the result is an unwieldy mess. And that’s just one of the problems with “You Again,” a perfectly awful movie about old high school enmities resuscitated during a wedding celebration. How bad is it? If it were a new TV sitcom, it would be cancelled after a single episode.

The set-up is that successful PR executive Marni (Kristen Bell) goes home for the wedding of her older brother Will (Jimmy Wolk), only to discover that the girl he’s marrying is none other than Joanna (Odette Yustman), the mean girl who made her life miserable in high school. To make matters worse, Joanna is now pretending to be the sweetest thing on the block, and has become the darling of Marni’s parents Gail (Jamie Lee Curtis) and Mark (Victor Gerber). And she pretends not even to recognize the girl she tormented.

Okay so far, even if it’s hardly the greatest premise in the world. But when Joanna’s aunt Ramona (Sigourney Weaver) shows up—a rich, sophisticated hotelier—she turns out to be Gail’s onetime BFF in high school, though they had a terrible tiff at senior prom and haven’t spoken since.

What follows is a double track farce. On one track, Marni aims to unmask Joanna for the nasty person she is and thereby derail her brother’s plan to marry her. On the other, plain mom Gail tries to compete with the now smooth, confident and voluptuous Ramona. Both of these plot lines are supposed to be hilarious, but they’re filled with such lame confrontations, clumsy slapstick and idiotic twists that they’re crushingly annoying rather than amusing.

That’s not the end of the coincidences, either. At the very end yet another “surprising” old rivalry emerges between Marni’s “delightfully” horny grandmother (inevitably these days, Betty White) and her old rival played by Cloris Leachman—a concluding capper that’s more like the last nail in the coffin. And that’s not even considering the further thread involving nutbag Tim (Kyle Bornheimer), an old college flame of Joanna’s, still carrying the torch for her, whom the wedding party just happens to bump into on the street! (Of course, he also proves to be the assistant to the couple’s supposedly famous wedding planner, played by Kristin Chenoweth).

This brainless folderol—laboriously plotted and festooned with repartee of the most witless sort imaginable—is directed with a sledgehammer by Andy Fickman, who italicizes every lousy joke and moronic gag (including at one point a monumentally awful musical number) as though it were comic gold. And he extracts horrendous performances from everyone. Bornheimer is in a class by himself as the obnoxious stalker, but in their much larger roles both Bell and Curtis completely embarrass themselves with their grotesque mugging, and Weaver and Yustman aren’t far behind. By contrast the men of the house (and the cute guy who’s Marni’s obvious intended, played by Sean Wing) are utterly bland and forgettable, except for Billy Unger as Marni’s pro forma precocious younger brother Ben, who’s just irritating. As for White and Chenoweth, they merely do their usual shtick to ever diminishing returns. I know that White has achieved the status of a national icon, but her recent turns suggest that her feisty old lady act is getting really tired. There are also cameos by Dwayne Johnson and Patrick Duffy that add nothing of consequence.

The picture doesn’t even look good. It’s garish and chintzy, and in some early sequences David Hennings’ camerawork is so jerky that you’d swear the Blair Witch might pop up. Add to that Nathan Wang’s excruciatingly bubbly score, which lets no point pass unemphasized, and get a completely dire package.

“You Again” closes with a slew of apologies among the characters. But the one that’s really needed is from the filmmakers to the audience.