You wouldn't think a guy who could easily pass as a creepy pedophile walking around with a baby in a papoose pouch would be funny, but it is. I wasn't sure if I'd find this movie to be funny, but I did.
There are no secrets here, all you have to do is watch the trailer, or look at the movie poster to know what's going on. It's Las Vegas, it's a group of guys, alcohol is involved. Let the hilarity ensue. It may not be original, and despite their best efforts for coming up with zany gags and outrageous situations, it's still pretty predictable, but some fresh twists help keep a somewhat tired formula from feeling entirely played.
Doug (Justin Bartha) is getting married. On the weekend before he takes the leap, his best pals, Phil (Bradley Cooper) and Stu (Ed Helms), and his new brother-in-law, Alan (Zach Galifianakis) are going to take him on a road trip to Vegas for one last night of bachelorhood and debauchery. Phil is a teacher at a private school who is the James Dean of the group, while Stu is a conservative dentist who has to lie to his girlfriend in order to get permission from her to go (he tells her the guys will be in California wine country). Alan is the newest member of the group and the odd man out, though he is taken in to the brood and under the wing of Phil, whom he admires most. On the rooftop of their Las Vegas hotel the four men toast to the night they're about to have.The next thing we see are Phil, Stu (who is now missing a tooth), and Alan awaken to a trashed hotel room and a hell of a hangover, including no memory of what had transpired the night before. Before long, the three men realize Doug is missing. In the quest to find Doug, the events of the previous night are revealed mutually to our main characters and the audience. The film does drag a bit, especially toward the end of the 2nd act, but not enough to bring down the film.
None of the events of the night are fully revealed, such as through flashback, which is smart. After all, this is a film not about the night, but the morning (and day) after. The only time we see what really happened is during the credits as a montage of pictures plays through. It says both good and bad things for the film that this is one of the funniest moments.