"Most critics are cynical assholes," a character opines late in "Big Daddy," at just about the moment in the movie when a critic's jaded boredom with vomit jokes and treacly life lessons might indeed be kicking in. Call it a preemptive strike on the part of star and co-writer Adam Sandler. Because he may be an asshole, but one thing you can never accuse Sandler of is cynicism.

Sandler -- who, since his "Saturday Night Live" days, has displayed a particular talent for portraying some of the most gratingly annoying characters ever beamed through a cathode ray or projected onto a screen -- is, in many ways, your typical $20 million-a-picture comedic jerk. No matter what the vehicle, his role rarely varies -- he's the schmuck with vast stores of hostility just waiting to be farcically tapped. In this regard, he's not much different from the oafs Jim Carrey used to play before going off to become a serious actor, or the bodily function-obsessed menfolk of the Farrelly brothers' early oeuvre. Yet despite his cinematic flair for beating Bob Barker senseless with a golf club or terrorizing the guests at a nuptial feast with a snarling version of "Love Stinks," Sandler always remains, at the heart of things, an old softy -- a man who loves grandmas, little children and pretty ladies who don't care how big a flake he is.

Sonny Kofax, the hero of "Big Daddy," is Sandler's standard alter ego -- a 30-ish underachiever who threw away his law degree to become a one-day-a-week toll booth worker. His dad nags him to get a real job; his roommate's fiancie, Corinne (Leslie Mann, who appeared in "George of the Jungle"), thinks he's a parasite; and his careerist vixen girlfriend, Vanessa (Kristy Swanson), is so fed up with his so-called lifestyle she's ready to put him on the train to Dumpsville. But Sonny is more than a mere lumpen mass of ESPN-watching inertia. He's sensitive, gay-friendly and mentally nimble enough to give legal advice to his attorney friends. Little surprise, then, that when an adorable 5-year-old orphan (played by twins Cole and Dylan Sprouse) appears on his doorstep, Sonny melts faster than gum on hot pavement. It doesn't hurt that he thinks adopting the tyke can change Vanessa's mind about breaking up with him.

It turns out that taking in a foundling is not in fact the best way to impress a woman, especially when one's dubious parenting skills could provide enough fodder for a week's worth of "Sally Jessy" episodes. Before long, Sonny is officially emancipated from Vanessa and bonds with his small charge in ways Dr. Spock never imagined -- he teaches young Julian the art of public urination, hauls him around to seedy bars, uses him as bait to pick up chicks in Central Park and feeds him multiple packets of ketchup for lunch. Surprisingly, none of Sonny's atypical child-rearing practices attract the notice of Social Services, until it's discovered that he isn't Julian's biological father -- at which point Sonny finds himself in danger of losing the one person he truly loves.

If all of this sounds a little schizophrenically formulaic, it is. An Adam Sandler movie always walks the line between cheap gags and surprisingly genuine sentiment, between white-hot coals of rage and warm chocolate pudding puddles of love. At times, the contradiction is pretty entertaining, especially when Sandler's working both sides of his persona simultaneously. There's something both jovially good-natured and undeniably deviant about taking a child trick-or-treating and browbeating a frightened homeowner out of his Rolex and CD collection. And it's hard not to be amused by a guardian whose overprotectiveness extends to interrogating a playground full of toddlers about their drug and alcohol use.

But for all "Big Daddy's" amiable and decidedly warped appeal, a comedy still succeeds or fails by how much it can make you laugh. And the film's jokes, stretched out over 90 minutes, aren't that funny. A running gag about Sonny's contempt for Corinne's past as a Hooters waitress falls flat the first time, but it's beaten into the ground and flogged lifeless. And the bucketsful of pee, spit and puke that litter the film seem naughty at first but soon become just plain tiresome.

Sandler and his fellow writers don't quite know what to do with the other members of the cast -- there's a foreign delivery guy (the consistently insufferable Rob Schneider), a weirdo homeless dude (Steve Buscemi, who had memorably hilarious cameos in "Billy Madison" and "The Wedding Singer," but strikes out here) and a cantankerous old barfly (Edmund Lyndeck) with the worst teeth this side of "Austin Powers." What movie are these characters supposed to be acting in? They have almost nothing to do with the plot, and their pathetic antics aren't funny enough to stand on their own as set pieces. They're just padding -- bad, bad padding. Finally, casting Leslie Mann and Joey Lauren Adams ("Chasing Amy") as squeaky-voiced sisters certainly scores points for believability, but add a small child wif his own weird wittle speech pattens to the mix, and you've got yourself a movie that at times makes you wish it were dubbed.

As we settle into yet another summer of doofuses (Austin and Jar Jar are just the beginning), Adam Sandler may yet emerge as a dork to be reckoned with. His aggressive crankiness appeals to anyone who's ever wanted to toss a stick in the path of a speeding roller blader, his innocently juvenile sense of humor speaks to those who can still work up a giggle over the word "poop" and his gentle concern for all things small and helpless speaks to those of us who like to believe that it's possible to possess both a decent soul and a certain vulgarity of character. It's a concept not without its sweet appeal -- if only it were a little wittier, I might actually be convinced.