The Hangover
Hands down the funniest movie of 2009, The Hangover is so outrageous the laughs plow right through its copious plot holes. (How the hell did they ever get that police car?)
In any case, the film's greatest strength resides with its temperamentally diverse cast. The three protagonists, who misplace the groom somewhere in Las Vegas the day before the wedding, are just incompatible enough to make their antics seem natural rather than contrived, which is often what gets a project like this in trouble. Without an experimental director like Todd Phillips, The Hangover just becomes another awful Robin Williams/John Travolta "comedy."
Phillips gives his actors a wide improvisational berth and Bradley
Cooper, Ed Helms and especially Zach Galifianakis take full advantage
of it while consciously not running too far afield of the plot and
their own characters' natural tendencies. It keeps the movie grounded
in its own reality as the groomsmen uncover the increasingly unlikely
and surreal events of the previous night, which in turn makes it
believable enough to laugh at unconditionally.