Watched it for a 4th time. Yeah, Howard just disrespected the blonde goon one too many times. The goon asked him to call Julia to get her back to the shop he straight hung up the phone and after he locked him in that vestibule area Howard told him to shut up. After that and sitting on the floor in a cramped space for an entire basketball game dude had enough. He decided when the game started he was going to kill him. And what's funny is they were leaving and that wedge fell out of the door giving Howard the idea to lock them in there. If the wedge never fell they leave he wins the bet, pays them off when they are calmer and lives. Great movie.