I always smile appreciatively. These same people courteously wait their turn in the grocery check-out line. The fuel savings help to partially defray the increased insurance premiums. For some reason, the studies revealed, Bulb-Savers have more accidents. Eight stereo speakers and a little extra volume really optimize my voice quality.
Some drivers play air guitar, air drums, or dance.
I gave those up for the sake of safety and now do vocals only. The most menacing form of this syndrome comes when combined with Tailgater behavior. These are people who always do the opposite of whatever a sign tells them to do. Spot them by looking for drool on their clothing. There are, of course, local variations to the above-described syndromes which are typically more pronounced the larger the city.