Grade: F

It’s appropriate that much of “Because I Say So” is set in a bakery, since even in a sea of awful chick flicks, this appalling confection takes the cake. The plot sounds like the script for a busted sitcom pilot. A buttinski mother, Daphne (Diane Keaton), places a personals ad to audition potential suitors for her unmarried youngest daughter Millie (Mandy Moore), a nervous, fast-talking and somewhat klutzy caterer. She finds what she considers a perfect candidate in smooth, ambitious architect Jason (Tom Everett Scott), but musician Johnny (Gabriel Macht) overhears her questioning of the guys, and though she thinks him amusing but unsuitable, he decides to contact the girl on her own. Predictable complications arise, from Johnny’s being a single dad to a precocious tyke (Ty Panitz) to the manipulative but unfulfilled Daphne’s falling for his easygoing father (Stephen Collins). And that’s small potatoes compared to the contrived crises that erupt when Johnny finds out Millie’s been dating Jason as well as him, and Millie finds out about her mother’s setting her up.

It’s difficult to decide what’s the worst part of this awful movie. The insulting jokes early on that offer crude stereotypes of Indians and Orientals, as well as an offhanded remark targeting gays? Moore’s hapless slapstick routines, or her embarrassing description of an orgasm toward the close, clearly intended as a comic highlight but coming across as crude imitation of Meg Ryan’s famous dinner scene in “When Harry Met Sally”? The ubiquitous reaction shots of Daphne’s dog, which are always a sign of directorial desperation, particularly when used in such profusion? The constant insertion of sequences involving Daphne and her three daughters out shopping or jabbering to one another on their cell phones—which, along with numerous shots of Daphne pawing around in her overstuffed purse or rearranging her furniture, are really insulting to women, making them all seem like brainless twits? Or the numerous instances of the kind of blandly naughty sexual moments that seem designed to make older female viewers titter in embarrassment?

No, the worst thing about “Because I Said So” is Keaton, who offers an exhibition of her customary nervous mannerisms magnified a thousand times over. True, she’s playing a character that’s intensely irritating; but she overplays the role so terribly that you actually have to resist lunging at the screen in an effort to throttle her. (And her big hyper-emotional monologue about an hour in is so calculated a plea for acceptance it almost makes you gag.) Moore, who’s given a few unwelcome opportunities to sing, is only marginally less annoying—she stumbles, trips and falls in futile efforts to elicit laughs almost as often as Keaton does—and as Daphne’s other daughters Lauren Graham and Piper Perabo are more tolerable only because they have less screen time.

Among the guys, Scott tries to play it mellow and slick with a touch of phoniness, but he never seems comfortable, and a brief scene with his caricature upper-class relatives is ghastly. As the single-dad guitarist and his father, Macht and Collins do little but smile indulgently at the female madness around them. It’s easy for them; they’re getting paychecks. Viewers who have to put down hard-earned cash at the boxoffice will understandably be far less tolerant. Indeed, the most likable figure on screen is young Panitz, who may be encouraged to act hyperactive but nonetheless comes across rather sweet, especially by comparison to the adults surrounding him.

From a technical perspective the movie is utterly mediocre, and it’s truly sad to realize that this clumsy mess was helmed by Michael Lehmann, who once gave us the tartly mean-spirited “Heathers.” A disaster like this makes that black high-school comedy seem like an eternity ago. And one grimaces repeatedly at the music choices, in which pop tunes are used to comment in the most unimaginative, heavy-handed fashion on the action, especially in dreadful montages.

From a cinematic perspective, this has been one of the most pathetic Januaries in many years. “Because I Said So” makes it a lot worse.