Plot hole: At closing time, Cliff, Norm and Woody spontaneously decide to go to Cliff's house. Sam then enters the bar after his date at Melville's. Later in the scene, Rebecca asks Sam about the 'Three Stooges', to which Sam sarcastically replies that they went to Cliff's house. But how could he possibly know that since he entered the scene after they had already left.
Other mistake: Right after Sam tells Carla he will sleep with the next woman who walks through the door, in the background there is an "Extra" (blonde-haired woman seen in background between Sam and Carla) who starts to cross right then turns and crosses lefts then turns right and stops and looks confused as to where she is to cross. Obviously she was given directions of which way to cross and when, but forgot.