If you've ever wondered how to spot a road rager, and their aggressive tailgating and sudden swerving of lanes while gesticulating in the cabin don't give it away, then the next best thing is to look for tacky accoutrements.
Social psychologist William Szlemko, of the Colorado State University, has concluded that motorists with bumper stickers, window decals, vanity license plates and other such "territorial markers" tend to get more incensed behind the wheel, and are more likely to express it.
His study also shows that the sentiments on the stickers don't matter. You could be cruising around with a "Free Tibet" sticker, and you'd still be as aggro as the guy rolling with "How's my driving? Call 1-800-UP-YOURS".
Szlemko does say that drivers who don't personalise their cars get angry too, but it's just more likely when you're talking about people with gaudy vinyl stickers and licence plates devised by the semi-literate. The more it's stickered up, the more likely the driver is to be aggressive.
If a walk down the local cruise strip of the major capital cities has shown me anything, it's that vanity plates seem to be like kryptonite towards driving ability. The stupider the word spelled, the worse the driver is at controlling their vehicle. I always thought that the more stickers and custom paint your car had, the lower the back of your seat went. If a car is painted a custom shade of candy paint with vinyl decals, the only thing you'll see through the driver's side window is the beak of a white baseball cap, and you'll have to look through the rear window to see the rest of the driver's head and the headrest.