Ben Stiller as a squeamish, dyspeptic, risk-aversive stiff? Unbelievable! A Jew with a big heart who gets nervous and defensive around taller, manlier goys? How bold! How sensationally out of character!

If the shoe fits, keep wearing it — that, at least, is the operating principle behind “Along Came Polly,” a comedy of mismatched temperaments that reunites Stiller with writer-
director John Hamburg, who also co-wrote Stiller's biggest hit, “Meet the Parents.” That Stiller virtually sleepwalks through his performance as a cuckolded newlywed who gets a new lease on love with a free-spirited, commitment-phobic waitress (Jennifer Aniston) is perhaps beside the point for bottom-line-minded viewers — the movie churns out jokes by the truckload, enough to keep us nominally amused even without the faintest hint of substance or wisdom.

Stiller (“Reality Bites”) plays ace risk-assessment manager Reuben Feffer, a man so fixated on life’s pitfalls that he can’t cross the street without calculating his chances of being hit by a car. That’s a solid foundation for a character, but doesn’t necessarily lend itself to facile physical comedy, so Hamburg also saddles Reuben with a cruel assortment of neurotic tics and inadequacies, including germ-a-phobia, irritable bowel syndrome and dance floor dorkiness. “Along Came Polly” is, in essence, a series of scenes in which we find Reuben in various states of embarrassment or discomfort. We see him unsuccessfully try to use a urinal alongside his hulking, immodest boss (Alec Baldwin, hilarious), getting a mouthful of another man’s perspiration during a pick-up basketball game, and wrinkling his nose at the disgusting personal habits of his best friend Sandy (Philip Seymour Hoffman, doing his best John Goodman impersonation), a pathetic loser still milking the fleeting fame he enjoyed as an iconic teen actor in a John Hughes-style “Breakfast Club” rip-off.

Most humiliating of all, the ink on their marriage license is barely dry when Reuben finds his new wife (Debra Messing from “Will & Grace”) engaged in extramarital water sports with a French scuba instructor (Hank Azaria). Heartbroken, he returns to New York and chances to meet Polly (Aniston), an old junior high school acquaintance who is everything his estranged wife is not — impulsive, fun-loving and bohemian. To curry favor with the decidedly spicy Polly, Reuben eats curry (yielding the movie’s single funniest scene) and tries to learn salsa dancing (yielding the least funny). Inevitably, the wife returns, contrite, looking to reconcile, forcing Reuben to decide who he really is and what he really wants.

We never really accept Reuben as a character — manufactured as he is to optimize jokes — but at least his implausible personality feels developed. The same can’t be said for Polly, who is so fickle that she extends Reuben an invitation for a date one second, and withdraws it the next. That’s more than commitment-phobic, that’s pathological, but we never really get a clear picture of where it comes from (later, she makes a vague reference to a runaway dad, but that’s it). Aniston is pleasant and competent in the role, but you get the feeling that Hamburg, who also co-wrote Stiller’s “Zoolander,” doesn't want to darken the light-hearted tenor of the movie by delving too deeply into her character.

Much of “Along Came Polly” simply misfires, including a subplot involving an extreme-sports-loving Australian business mogul (Bryan Brown from “FX”) on whom Reuben conducts a risk-assessment. Sure, there are a few chuckles, but if you try searching for any deeper meaning in this less-than-
stellar Stiller vehicle, the joke’s on you.