auto ventriloquism
Auto ventriloquism is the art of talking or signing to oneself without moving one's lips while driving an automobile.
Passenger: "Hey, look at the guy in the car next to us. What an uptight douche bag."
Driver: "He's not uptight, man. Look you can see his lips moving a little. He's practicing auto ventriloquism."
Driver: "He's not uptight, man. Look you can see his lips moving a little. He's practicing auto ventriloquism."