Weird things to do in cars because yelling is fucking annoying and you're an asshole for doing it (and so's your face)
In the "Let the audience listen" category...
(Wear earplugs)Buy Yodeling CDs, roll down your windows, crank it, and roll slow through a pedestrian area. Sing along.
Dress as a thug gangsta. Cruise slow, nodding your head to NPR. Bonus points if it's Science Friday. As above with the yodeling, windows down, volume up. The more people in the car dressed the same, the better.
In the "whadafukwasdat???" category
Wear superdark sunglasses. Park in a normal spot. Get out, unfold your walking stick
and tap your way around the lot.
Wear clown makeup. No wig, plain T-shirt, no funny tie... just clown makeup. You have no idea how ... odd.. that is until you see it. It helps if you have a happy face painted but look incredibly depressed.
Get two friends. It helps if you're all over 25. Dress as a Priest, a Rabbi, and a Buddhist Monk.