“It’s happened again,” Phil (Bradley Cooper) tells his wife early in this sequel to the first “Hangover,” which follows the rule for follow-ups once enunciated by “drive-in movie critic” Joe Bob Briggs—just make the same picture a second time. Even for those who liked the initial installment, the return trip isn’t likely to be as much fun.

Simply put, “The Hangover 2” copies the original so slavishly that it’s the equivalent of a big-screen rerun. The prospective groom this time, however, isn’t Doug (dull Justin Bartha), who was the lost puppy last time around, but milquetoast dentist Stu (Ed Helms), who’s dumped his shrewish girlfriend Melissa in favor of sweet Lauren (Jamie Chung). He’s planning to marry her in her native Thailand as a concession to her family, especially her rich father Fong (Nirut Sirichanya), who has contempt for him.

Unsurprisingly, the night before the planned ceremony brash, big-mouth Phil insists that Stu go with him, Doug and Doug’s now-brother-in-law, spaced-out Alan (Zach Galifianakis) for a beach bachelor party, taking along Lauren’s little brother Kenny (Mason Lee). Doug leaves early, but the next morning Phil, Stu and Alan awaken hung over in a dilapidated, disheveled room in a city that turns out to be Bangkok. Stu has a huge facial tattoo and Alan’s long hair has been shaved off. Instead of a tiger, there’s a nicely-attired monkey in the room. And Kenny is missing except for the dismembered finger with his Stanford ring on it (though why he has a class ring though he hasn’t graduated is a question). So the trio set off to find out what happened, retrieve Kenny and make their way back to the wedding on time.

It would be a tedious business to recount their adventures. They involve Russian drug dealers, an exotic dancer who (as one especially noxious revelation reveals) can do double duty, an American tattooist (Nick Cassavetes) and an elderly Buddhist monk. Also a crime lord (Paul Giamatti, in an embarrassing cameo) who turns out to be not all he seems, and smarmy crook Mr. Chow (Ken Jeong), who turns out to be at the center of everything. Even Mike Tyson shows up again. But what really dominates is the stream of raunchy gags (including a virtual avalanche of penis jokes), slapstick violence (which often takes a really nasty edge) and foul language en route to the preordained finale in which Stu delivers a ringing endorsement of his pals that seems win the irascible Fong over.

Why that should be the case is the big question you might have at the end, because frankly these guys continue to be a pretty repulsive lot. Phil is a reckless loudmouth, Stu a whining ninny, and Alan a stooge with a mean streak. And under Todd Phillips’ slapdash direction, of the actors only Helms has anything much to offer, since Cooper is a smiling cipher and Galifianakis one of those chubby guys who misses being lovable by a country mile. And though some apparently find Jeong’s wildly ripe take on a drugged-out goofball very funny, it’s a one-note bit that’s just sitcom stuff squared.

In Lawrence Sher’s cinematography “The Hangover 2” takes advantage of the Thai locations, from the beautiful beachfront wedding spot to the sleazy streets of Bangkok. One must say though, that the overall effect isn’t to make you want to visit the country. And unless the sight of a monkey smoking a cigarette drives you into peals of laughter, you’re probably best advised not to visit the movie, either.