It's a guilty pleasure comedy. Who knew a hangover could be this fun? In terms of concept and plot, this guy flick about a bachelor party gone wrong is nothing special; but the simplest reason for its comedic success is the fact that it achieves a rare balance between character and vulgarity in its storytelling. There is a sort of perverse brilliance, or maybe brilliant perversity, thrown by the characters against the gambling streets of Las Vegas. Director Todd Phillips ("Starsky and