‘Hangover III’ leaves a searing headache

The only reason Hollywood makes sequels and three-quels is because they’re presold — meaning they’re easy money — so all I have to do is type the words “Hangover Part III” and you already know if you’re in the ticket line or you’re out of there.

If you’ve seen the stunningly mirth-free trailer, chances are you’re out of there. But this third go-round for the “Wolf Pack” doesn’t bother to Xerox the original 2009 hit comedy, as 2011’s witless “Hangover 2” did. Instead, the new movie heads in different, if utterly formulaic, directions. So it’s not terrible. It’s just bad.

Ditching the stock set-up we’ve come to expect — our heroes waking up with no memories but plenty of bizarre evidence of the night before — “Hangover Part III” puts bad-boy Phil (Bradley Cooper), nervous-nellie Stu (Ed Helms), freaky man-child Alan (Zach Galifianakis), and the crew’s all-purpose Zeppo, Doug (Justin Bartha), on the road to the treatment center Alan has nervously agreed to check into. They’re hijacked midtrip by Marshall (John Goodman), a crime lord looking for the antic Asian gangster Mr. Chow (Ken Jeong). Chow has stolen his gold, and Marshall wants the boys to bring him, and it, back.

Keeping Doug as insurance (thus conveniently subtracting Zeppo from the movie), the kingpin sends the other three to Tijuana and then to Las Vegas, site of the first film’s mayhem, in search of Chow. There are visits with old friends — Heather Graham reprises her role as the nicest hooker in all of Nevada — but in all other respects, “Hangover Part III” is dully straightforward stuff, with none of the jack-in-the-trunk surprises and little of the inspired crassness of the original “Hangover.”

By the scene 45 minutes in where Chow and Stu break into a house and argue over which alarm wire to cut, you know this series is running on fumes.

Occasional chuckles leak out, almost all of them because of Galifianakis’s man-from-Mars line readings and body language. Melissa McCarthy cameos as a Vegas pawn shop owner who might be the girl of Alan’s twisted dreams, and she and Galifianakis play nicely together: two hardcore narcissists in love.

But far too much of “Hangover Part III” hangs on the notion that you find Jeong’s pansy-pottymouth schtick funny, and that’s asking a lot. The actor has built a successful career as a character irritant, but a little of him goes a long way, and most of it got used up in the first “Hangover.”

What’s really missing from “Part III” is the sense of comic outrage — the knowledge that around every corner something bigger, weirder, and more disastrous is awaiting the characters. (A tiger, Mike Tyson — whatever.) Here it is smaller and more predictable.

The only time this movie truly ascends to the heights of low humor is in the end-credit sequence where, traditionally, we find out what really happened the night before. This time we learn what happens the morning after the gang’s next wedding, and it’s a sight gag that shall not (and in a family newspaper, cannot) be spoiled. It’s almost enough to make you wish for a “Hangover Part IV.” But not really.