In my adventures trying to find a sensible liberal blog, where issues are discussed, even if not always politely (Ed: Not like you, huh?), I was accused of making this one up. My point in the discussion was that hate speech and incitement to violence were more prevalent on the left, having penetrated from the leftist fringe to the average Democrat (the owner of the car with this sticker has a Master's degree and is a socially graceful coworker). The equivalent on the Right, those with the "I Don't Brake For Liberals" stickers remain on the fringe.
Actually, it's not a bad site, and I will write up my adventure, and a lesson learned, soon. For now, here's the bumper sticker that doesn't exist. Imagine zipping in the name "Jesse Jackson" or "Hillary Clinton," if you still think it's just lighthearted humor.