I just saw this on the car in front of me today:
Back off or I'll flick a booger on your windshield
Here's my all-time favorite bumper sticker story. One day 30 years or so ago when my brother and I were teenagers we were riding with my mother (a dear, sweet innocent lady who didn't have a filthy bone in her body). The car in front had a sticker that read, Save a tree. Eat a beaver. As my brother and I gaped bug-eyed, she stared with wrinkled brow then finally mused out loud, Well, I guess beavers do kill a lot of trees...