Most of it plays like Jackass.
Beginning with a dramatic escape from a Bangkok prison, The Hangover Part III shifts its focus away from the Wolfpack - fast friends Phil (Bradley Cooper), Stu (Ed Helms), and Alan (Zach Galifianakis) - to the lunatic Leslie Chow (Ken Jeong), the little cokehead crime boss who popped out of the car trunk, naked, in the first film and returned to wreak more havoc in the sequel.
His role is greatly expanded in Part III, beginning with the aforementioned Thai jail break. In fact, the reason Phil, Stu, and Alan find themselves first in Tijuana and then returning to Las Vegas is that they've been given three days to deliver Chow to a rival gangster (John Goodman), or else they'll never see their best bud, Doug (Justin Bartha), alive again.
If the original Hangover pushed the envelope of R-rated comedy to the outer limits - roofies in the drinks, a tiger in the bathroom, a baby in the closet, and Mike Tyson in a rage - it also delivered an adrenalized rush. The craziness felt inspired, not contrived. It was exhilarating watching Cooper, Helms, and Galifianakis react to one nutball scenario after another - the actors as startled by what was happening as the characters they played.
By now, though, the studly Phil, the mild-mannered Stu, and the pampered wacko Alan - off his meds, and off his rocker - have become cartoon versions of their former selves. And the best gags (like Alan delivering "Ave Maria" operatically, at a funeral) have been playing for weeks in ads and trailers, the surprise sapped.
Part III's writing team, headed by Phillips and Craig Mazin, pile on the extreme-comedy gags, from a catastrophic interstate crack-up involving a giraffe to a scuffle between cockfighting roosters and humans that ends with one of them (one of the roosters, that is) being suffocated with a pillow. To quote a line from the movie, bad things happen and people get hurt.
Animals get hurt, too.
Part III, mercifully, feels like the final chapter - the guys walking off in slow-mo, in a mock-heroic montage culled from all three Hangovers. But if the movie realizes the kind of box office numbers the studio clearly expects it to, who knows, maybe there will be a Hangover IV.
Even more Ken Jeong? Talk about headaches.
The Hangover Part III ** (out of four stars)
Directed by Todd Phillips. With Bradley Cooper, Ed Helms, Zach Galifianakis, John Goodman, and Ken Jeong. Distributed by Warner Bros.
Running time: 1 hour, 40 mins.
Parent's guide: R (violence, profanity, nudity, drugs, adult themes, giraffe abuse)
Playing at: area theaters
Contact Steven Rea at 215-854-5629 or email@example.com, or follow on Twitter @Steven_Rea. Read his blog, "On Movies Online," at www.inquirer.com/onmovies.