Looking tired and sallow and drained of her customary glow, Lindsay Lohan marches grimly through this mechanical ‘tween comedy as if it were a particularly tedious homework assignment. Which it is: The kind of switch- eroo premise that so deftly showcased Lohan’s gift for physical comedy in Freaky Friday falls flat as a pancake in this lame slice of slapstick about a Manhattanite whose habitual good luck runs out when she kisses a luckless stranger (the anodyne Chris Pine) who’s trying in vain to make it as a rock producer. As his good fortune waxes, hers wanes, thus exposing them both to a rapid succession of excruciating sight gags involving dog poop, cat poop, and endless rain without benefit of an umbrella. Just My Luck is so unremittingly chipper, you’ll want to shoot it on sight. Lohan is a great talent whose gravel-voiced poise promises an intriguing transition from child performer to young siren, but if she continues to lend herself to rubbish like this, she’ll be remembered as no more than a sad little party animal.