Best bumper sticker I've seen so far: "either you're an entymologist, or you have suicidal tendencies and need help". No one in my family got this until I explained it, which was hard, as I couldn't stop laughing.

On another bumper-related note, I've noticed that all the non-vanity license plates I've seen in California (with the exception of large vans) have the same format - 1 number, 3 letters, 3 numbers. Example: our rental car's plate is 5GFD803. Weird.