Director Todd Phillips (“Old School,” “Road Trip”) and screenwriters Jon Lucas and Scott Moore (“Ghosts of Girlfriends Past,” “Four Christmases”) surpass those four comedies with this smart vulgarity set in Vegas. A knowing nod is found in Phillips’ variant on his possessory credit: “A Todd Phillips Movie” (instead of “Film.”) The humor seesaws from clever to crude. Doug the groom (Justin Bartha) and two college buddies—Phil, a high school teacher (Bradley Cooper), and Stu, a dentist (Ed Helms)—steer a silver 1969 Mercedes Benz convertible to Las Vegas two days before Doug’s wedding. The vintage wheels belong to Doug’s father-in-law, who stipulates that his son Alan (Zach Galifianakis) not drive. Alan, though, is the comic driveshaft here. When the foursome check into Caesar’s Palace, he tries to impress the front-desk clerk with a savvy inquiry about the real palace where Caesar stayed. Later, the usually mild-mannered Stu will yell at Alan, who makes comparably dumb inquiries about the Holocaust and Halley’s Comet: “You are literally too stupid to insult!” Typical of the right tone in “The Hangover” are times when characters laugh at other characters: an effeminate Chinese thug (Ken Jeong) finds fat Alan funny. On the rude side there’s a baby made to look like he’s masturbating who gets a car door slammed on his head. Memory-loss due to Rohypnol-spiked shots of Jagermeister shapes an original plot linking a trashed $4,200-a-night suite, tiger theft and a missing lateral incisor. With Heather Graham, Mike Epps, Jeffrey Tambor, Mike Tyson. 96m. Anamorphic 2.40 widescreen. (Bill Stamets)