I was discussing these cards w/ a guy at work who was a kid when they first came out. He insisted that, for all the horror and gore in the whole set, that ^this was the card that got the entire series pulled from the shelves in a matter of months. I'm inclined to believe him.
http://en.wikipedia.org/wiki/Mars_Attacks
http://www.tradercracks.com/gallery/non-sports/Mars_Attacks/