I don't know how common bumper stickers are outside of the united states so let me explain: They are stickers that go on the back bumper of your car that usually have short, witty remarks!
I want to know what your favorite bumper stickers are!
I'll start with a few of my favorite:

1) "visualize whirled peas!"

2) This was seen on a motor home today! It said "Trespassers will be shot! Survivors will be shot again!"

3)"Jesus saves sinners, and redeems them for valuable cash prizes!"

4) "Defoliate Bush!"

What are some of the ones you have seen over the years that tickled your funny bone, or you that particularly clever?