A backseat DUI occurres when a sober person is driving an intoxicated person home, and the intoxicated individual is giving the driver shitty directions, and false instructions to turn, and then saying "No, No, not this street..."
This causes the driver to
speed up, slow down, and begin to turn, then
swerve back into the driving
lane, leading others observing the vehicle from the outside to believe that the driver is DUI.