Ray Wylie Hubbard's song Up Against The Wall Redneck Mother has a line about a pick-up truck with a bumper sticker. Many folks seem to insert their favourite bumper sticker quote in this line.
One (by Willie Nelson?) said, "I'd rather step in shit than smoke it."

It reminded me of some anti-vegetarian bumper stickers seen in Northern Ontario: "If we're not supposed to eat animals, how come they're made out of meat?" and "There's a place for all of God's creatures...right next to the mashed potatoes."