What happens in Vegas doesn't always stay in Vegas, thankfully. Otherwise we'd be without "The Hangover," and our summer wouldn't be quite so amusing.

Directed by Todd Phillips of "Old School" fame, "The Hangover" is raucous and politically incorrect, and it's so frequently funny that the viewer will soon forget about the jokes that fall flat or linger too long.

The story follows three best friends — plus one hanger-on, the soon-to-be-groom's future brother-in-law — who go to Vegas for an unforgettable night of debauchery before one of them is married.

When morning arrives, however, none of them can remember a thing, the hotel room has been trashed, there's a tiger in the bathroom, and the groom is missing.

For the rest of the movie, the remaining three amigos seek out clues and try to reconstruct just what happened, with hilarious consequences.

The budget cast of "I know that guy from somewhere" actors — plus Heather Graham, in a part small enough that she can't ruin the film, and Mike Tyson in a winning cameo — fits just right. Ed Helms ("The Office") is the standout as a nerdy dentist with a shrewish girlfriend (and he gets in one killer song too). Bradley Cooper is the good-looking rogue, Phil. Justin Bartha ("National Treasure") is Doug, the most responsible, normal and well-grounded of the group, who fortunately disappears for much of the movie.

Relative unknown Zach Galifianakis is the off-kilter, slightly addled future brother-in-law Alan, who is granted most of the best lines. He's uncomfortably funny, but I could also picture several other actors doing it better with the same material. It's the kind of part John Belushi would have had a generation ago.

"The Hangover" is rarely in good taste — and it clinches the 2009 "Borat" award for uncomfortable scenes of male nudity — but it has plenty of surprises, and it doesn't ease up at any point. It's one of the best comedies of the year thus far.

Rental Recommendation: Bradley Cooper can also be seen in another R-rated laugh fest, as the bullying boyfriend in "Wedding Crashers." Grade: B+.

E-mail Steve Ouellette at: ouellette1918@gmail.com