Real bumper stickers found on real cars:

Horn broken. Watch for finger

Your kid may be an honors student, but you're still an idiot.

Forget about World Peace... Visualize using your turn signal.

Change is inevitable, except from a vending machine.

Cover me. I'm changing lanes.

I brake for no apparent reason.

Lottery: A tax on people who are bad at math.

I'm not as think as you drunk I am.

Learn from your parents' mistakes - use birth control.