The Whole Nine Yards (2000)

Jimmy "The Tulip" Tudeski (Bruce Willis), a mob hitman-turned-informant, ratted on the mob and put his life in jeopardy. Now he has moved to suburban Montreal, ostensibly to make a new start. His next-door neighbor is mild-mannered, unhappily married dentist Nick "Oz" Oseransk (Matthew Perry). Nick recognizes Jimmy from the newspaper stories about his mob testimony, and that's when Nick's simple, boring world turns upside down.