Todd Phillips may never be afforded the same respect as his more venerated peers, if only because directors who spend their careers chronicling the foolishness of badly behaving men rarely do. But it’s hard to ignore his track record.

Save for his remake of Robert Hamer’s 1960 comedy School for Scoundrels, unseen by me but roundly dismissed by others, Phillips has earned justified praise for his affable depictions of testosterone-driven silliness in movies like Road Trip and Old School. The Hangover finds him going to the well once more, with results that are laughably deranged but hardly preposterous to anyone who’s ever lost a weekend in Vegas.

Doug (Justin Bartha) is getting married. Reaction to the news is mixed – Stu (Ed Helms, of NBC’s The Office), who yearns to settle down himself, is thrilled, while Phil (Bradley Cooper), already a husband and father, champions the benefits of bachelorhood. But on one thing they agree: There’s going to be party, far removed from the prying eyes of girlfriends and wives.

A self-described “wolfpack of one” and the resident oddball of the bunch, Alan (Zach Galifianakis) is happy just to be included. Short, stocky and sporting a Grizzly Adams beard, Alan is also the most interesting of the lot, precisely because he doesn’t fit an obvious stereotype. Socially uncomfortable but far from introverted, he is a cheerful enigma, as likely to break the casino’s bank as he is to wonder aloud, without irony, whether Caesar’s Palace once housed the emperor himself.

If Alan seems every bit as eccentric as the colorful cast of cops, crooks and flamboyant hustlers he encounters during a bleary-eyed tour of Sin City, Stu and Phil are cut from more familiar cloth. Stu, who looks and acts like a middle-aged McLovin, is a dentist hopelessly emasculated by his domineering girlfriend. Phil is tanned, handsome and endlessly self-assured, but claims to be dying a little with each passing day. Marriage, he says, is smothering his spirit.

After an evening of Jagermeister shots, strip clubs and delightfully subversive debauchery, Stu, Phil and Alan awake to find their $4,200 suite in shambles. There’s a baby in the closet, a still-smoldering chair in the living room and a snarling tiger in the bathroom. There’s a live chicken, whose presence is never properly explained, and a towering arrangement of empty champagne bottles. And conspicuously absent is the groom-to-be.

The Hangover follows Stu, Phil and Alan as they piece together their wild night, one hazy memory at a time. That their grueling journey serves as a much-needed shock to the system for each of them should come as no surprise – Phillips, like Judd Apatow, has often treated hedonism as a roundabout path to self-discovery, though with a minimum of Apatow’s forced sentimentality. Here, Phillips looks to find the humor in the desperate plight of his befuddled heroes, and he succeeds.

It’s a testament to Phillips, his cast and a surprisingly clever script by Jon Lucas and Scott Moore (Ghosts of Girlfriends Past) that we actually come to care about Doug’s whereabouts, not to mention the outlandish circumstances that leave Stu missing a tooth and Alan his beloved man-purse. (“It’s a satchel!”) But even if we didn’t, The Hangover would work nearly as well.

Far-fetched as their misadventures might seem, Stu, Phil and Alan are never reduced to hysterical caricatures or hard-partying dopes. They seem bright, reasonable and understandably floored by their own irresponsibility. Rather than taking us to the party, as Phillips did so often in Old School, The Hangover shows us the ugly aftermath. Everybody’s a little older, a little wiser, and a little disgusted with themselves the next day.

This is a comedy that manages to stay grounded despite itself, filled with agreeably nonsensical setups and wickedly funny payoffs. Dirty as it seems, especially during an inspired closing-credit sequence I will refrain from describing, The Hangover rarely relies on cheap thrills or shocking sight gags. Instead, Phillips defers to the playful chemistry of his stars, who make even the most ludicrous scenarios somehow believable. It’s a neat trick, making this Vegas vacation one to remember.