The old switcheroo is a common plot device in movies–characters have regularly exchanged identities, even bodies on occasion. Lindsay Lohan, in fact, has specialized in such trifles, going with the first in the remake of “The Parent Trap” and the second in that of “Freaky Friday.” But none of the switches has been quite as silly as that serving as the driving force behind “Just My Luck,” in which Lohan, playing Ashley Albright, a girl who’s always been on the right side of the fickle finger of fate, suddenly finds herself saddled with just the reverse after she kisses Jake Hardin (Chris Pine), a hapless sad sack who’s had nothing but the worst fortune until he gets the gal’s good vibe as a result of that smooch. The rest of the movie has Lohan’s character trying to track down the guy–unsuccessfully until she just bumps into him again (given that the story’s set in New York City, that’s the sort of massive coincidence known as Movie Fate) and get her good luck back from him. The predictable result is that by then they’ve fallen for each other and eventually are both willing to sacrifice the Midas Touch for the sake of Love.

Romantic comedies have certainly gotten by on ridiculous premises before, and though this one isn’t much more idiotic than others, it bears fewer dividends here than is the case with its better predecessors. That’s because scripters I. Marlene King and Amy B. Harris haven’t managed to come up with come up with anything besides a string of uninspired slapstick routines, occasionally punctuated of course by “nice” moments designed to sweeten the mix; because neither Lohan nor Pine seems particularly gifted in such knockabout stuff (though they’re likable enough making moon-eyes at oneanother); and because Donald Petrie doesn’t prove especially adept at staging it. “Just My Luck” is decently appointed (Ray Kluga’s production design and Dean Semler’s cinematography don’t make it look like a top-flight effort, but at least it doesn’t look mangy), but it comes across as limp. The Brit band McFly provides a few up moments as the unknown group that would-be manager Jake takes to the threshold of big-time success when his new-found good fortune allows him to save the life of music bigwig Damon Phillips (Faizon Love, who provides an outsized portrait of a tycoon). But the supporting cast, which carried a lot of the heavy comic load in the old romantic comedies made by the likes of Ross Hunter, is surprisingly weak, with Samaire Armstrong and Bree Turner not making much of an impression as Ashley’s pals, Missi Pyle arch and unfunny as her hard-bitten boss, and veteran Tovah Feldshuh not getting any laughs as the fortune-teller who clues Ashley in to what’s happening to her.

There are a few moments in “Just My Luck” that seem almost incomprehensibly misguided. (A vomit scene involving the band members is certainly one, but even worse is a gallery opening to which a rich playboy takes Ashley, at which all the pieces are made out of mud and a musical number is performed in which the dancers call themselves “mud people”–a truly grotesque reference for anyone even vaguely aware of the ideas of white supremacist groups.) Most of the time, though, it’s merely a flat, lackadaisical take on the supernatural love-story formula, lacking either the storytelling magic or the intense romantic chemistry that might have helped it take flight. A movie like this should soar, but this one just lumbers along, leaving its luck motif seem a lot dumber than it should have.