California Code, Vehicle Code - VEH § 21701

No person shall wilfully interfere with the driver of a vehicle or with the mechanism thereof in such manner as to affect the driver's control of the vehicle. The provisions of this section shall not apply to a drivers' license examiner or other employee of the Department of Motor Vehicles when conducting the road or driving test of an applicant for a driver's license nor to a person giving instruction as a part of a course in driver training conducted by a public school, educational institution or a driver training school licensed by the Department of Motor Vehicles.