"The Hangover" (2009) is directed by Todd Phillips, and co-written by Jon Lucas and Scott Moore. It is a absolutely hilarious tale of the misadventures of four men who, in effort to give their friend one of the best bachelor's parties a man can have, end up making a few detours along the way. It leads them through a day of trying to remember all the details of the previous night, this broken memory being where the movie derives most its humor from.
The movie is rated R for pervasive language, sexual content including nudity, and some drug material, though the language is not quite so bad as some would believe; yes, there is constant swearing throughout, but given the mens' situations, I think we can all give them a little lee-way (especially at one point where their memory--or what's left of it---is a matter of life and death). The sexual content is very mild throughout the actual film (an innuendo with a tiger and an exposed breast in one scene, basically mild stuff); however, the credits and their photo reel depict some less appropriate material. And the drug material? It's a movie, get over it. Learn the difference between the real world and the cinematic world.
If you want to see an absolutely hilarious film, with a very good moral mind you, then you will delight as you watch "The Hangover"; I say this film is good for viewers thirteen and up (just don't bring any very young children).