As with most subjects, almost everything I know about Las Vegas I've learned from the movies, which usually make our favorite oasis look like a tawdry, treeless hellhole, glittering with illegal activity and weatherbeaten sluts. That salaciously fascinating backdrop, especially when combined with the ominous "What happens in Vegas..." slogan, is a perfect setting for dark comedies in which people descend upon Sin City, get wrecked, and then do very bad things; 1998's "Very Bad Things," for example. And though the bumbling trio at the heart of director Todd Phillips' raunchy "The Hangover" doesn't actually off any hookers, their ill-advised behavior and its hilariously surreal consequences are the sorts of details that were probably meant to stay in Vegas.

"Whose fucking baby is that?" is but one of the many mysteries that need solving the morning of "The Hangover," along with the whereabouts of a tooth, how the tiger wound up in the hotel bathroom, and what might have happened to future groom Doug (Justin Bartha, "National Treasure"), gone AWOL during the drug-and-alcohol fueled mayhem of the previous evening's bachelor party. Phillips structures the bulk of his film in flashback, introducing us to smirky Phil (Bradley Cooper, "The Wedding Crashers"), pussywhipped Stu (Ed Helms, "The Office"), and gonzo Alan (Zach Galifianakis, "The Comedians of Comedy") as they're trying to piece together the hazy events leading up to their current predicament, which is standing in the desert and making a phone call to an understandably annoyed bride-to-be.

Setting "The Hangover" apart from the parade of filthy bromances is its clever assembly, which keeps us very engaged as we come by information only when our heroes do, allowing both us and them to be blindsided by shocking bursts of violence that alternate with ridiculous sight gags and bizarre humor, and occasionally all three when Ken Jeong's fey gangster Mr. Chow is involved. But most of the laughs come courtesy of the scene-stealing Galifianakis, who fearlessly mines comedy gold from his furry Snoopy shape and gets rewarded with the funniest non sequiturs, clarifying that counting cards is not illegal but frowned upon ("like masturbating on an airplane") and nonchalantly tossing off an honest-to-goodness Holocaust joke.

Phillips, who directed the similarly themed men-will-be-boys comedy "Old School," is sadly unable to do right by the ladies, represented in "The Hangover" by familiar stereotypes: the castrating shrew, the pliable bride, and the stripper with the heart of gold (Heather Graham, now flashing nipple for a good role, a la Marisa Tomei). It's not all Phillips' fault, though; he's working from a script by Jon Lucas and Scott Moore, who admittedly fare much better here - despite the clichéd females and just-shy-of-offensiveness - than their lame work on "Ghosts of Girlfriends Past." "The Hangover" is able to maintain its manic pace for an admirably long time, and just when it seems like you endured the headache and nausea for a sappily-ever-after, enter the sidesplitting end credits, with the answers you only think you wanted. Hair of the dog, people.

The Hangover

(R), directed by Todd Phillips

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