To smile at someone else in a car with flirtatious intentions. Usually in a traffic jam or at the lights when you notice someone you think is hot and they see you, a "car smile" is a way of letting someone know you like them.
In Ally McBeal she sees a guy at the lights and smiles at him, he just drives off and she get irate because "i gave him car smile" but he drove off uninterested, until she purposefully crashes her car into him to get attention.
by Jon1985 March 20, 2007