This is due the lethal combination of open windows and high speeds. The Driver is then referenced as a "douche bag", especially if it is done intentionally.
This can also be done as a deterrent for driving someone that the Driver particularly doesn't like driving around. As well the Driver reserves the right to pretend like they can't hear the person in the back seat, pleading for mercy.
Joe:"Man, Jake was being such a douche bag."
Gary: "Awe, pulling the old Backseat Air eh?"
Backseat Occupant: "Yo! Roll up the windows!"
Driver: "WHAT!? I CAN'T HEAR YOU!"
Backseat Air Backseat Air Driver