Bumper stickers are hilarious. "If the screams from my trunk bother you, turn up your radio"? Side-splitting. 'I'm not stupid, I'm hard of thinking'? Classic.
But psychologists in Colorado have discovered a high correlation between bumper stickers and road rage. Really. More bumper stickers equal more rage.
And, even more intriguingly, it doesn't matter what's on the stickers: angry slogans, hilarious one-liners, messages of world peace. Sticky bumper, angry brain.
The study tells us that the bumper sticker is used as something that marks territory, personalising the car in the same way as vanity plates and decals and making the driver more likely to defend their territory.
"We have a lot of instincts that animals have," says William Szlemko, co-author of the study. "Many people respond as if the violation took place in their home and not on a public road."
So unless you want people thinking you're a cleaver-wielding nutjob, you'd better peel off that "My Other Car is a Bus" as quick as you can.
That said, we've always found the shotgun/back window correlation a rather clearer indication of likely road manners.
Source: Top Gear