Fall down funny.  Unbelievable performances from Robert Downey Jr as a Russell Crowe character playing a black sargent ("i'm the dude playing the dude playing another dude"). and Tom Cruise as the ruthless Hollywood producer - his "you don't know me like that" dance at the end almost killed me.  Ben Stiller playing Simple Jack for an audience of heroin smgglers, over and over was pretty damn funny as well.  One of the funniest movies I have ever seen.