When things go wrong for us, it’s tragedy. When they go wrong for someone else, it’s funny. As Alan Dale says, comedy is a man in trouble. This comedy gives us four men in a lot of trouble following a debauched, drug-fueled bachelor party in Las Vegas who wake up with no recollection of what happened and no idea what has happened to one’s missing tooth, another’s missing mattress, and, most significantly, no groom. The one whose wedding is being celebrated, the one whose wedding is taking place the next day, has disappeared.

Meanwhile, there are some items in the trashed hotel room with the still-smoking chair that no one recalls having seen before, including a chicken, a tiger, and an infant. At the beginning of the evening, they toasted “to a night the four of us will never forget.” By the next morning, the three remaining guys cannot remember anything that happened, and the rest of the movie has them racing all over to figure out where they went, what they did, and how the groom managed to disappear without a trace.

In one respect, it’s just a cheerfully outrageous comedy, with much of the humor coming from our discovering along with the hapless trio of boy-men chafing at the bonds of civilization just how appallingly they have violated every possible standard of appropriate behavior and good taste. It’s your basic best of both worlds comedy where we get to see our most childish wishes fulfilled and then get to see the characters on screen suffer the punishment for it. But it is also a whacked-out variation on “The Wizard of Oz,” with characters in need of a heart, a brain, and courage going on a journey to an exotic land and learning that there’s no place like home.

Doug (Justin Bartha) is about to get married and so his two best friends take him to Las Vegas for one last bachelor blow-out. They are Phil (Bradley Cooper), a teacher who is married with a son and says that he hates his life in need of a heart, and Stu (“The Office’s” Ed Helms) an uptight dentist who is about to propose to his controlling, unfaithful shrew of a girlfriend, who needs some nerve. That leaves Alan (comedian Zach Galifianakis) who is lacking brains. He’s along for the ride because he is the bride’s brother. And the gorgeous mint-condition Mercedes convertible is what they are riding in, thanks to what is inevitably going to be shown to be a very foolish gesture on the part of the prospective father-in-law. The wicked witch part, of course, is shared by nearly every woman on screen.

Cooper is a comic actor trapped in the very appealing body of a leading man and Helms (who gamely had his fake tooth removed for authenticity) provides able counterpoint as the conflicted Stu. Galifianakis looks like a cross between a Hobbit and a garden gnome and a little of him goes a long way, but he manages to be less obnoxious than expected. And they run into an engaging variety of characters along the way including an emergency room doctor, a drug dealer (Mike Epps), an effeminate gangster, an earthy wedding chapel manager, and of course an “escort” with a heart of good (a very game and, as ever, alluring and adorable Heather Graham).

The film’s most disappointing element is its casual sexism. Aside from the escort, all of the women come across as shrewish and narcissistic. But other than that, like predecessors “Superbad” and “Pineapple Express,” the movie has an essential sweetness that disinfects its raunchiest moments.