Surely you've heard, too many times by now, about the radio transmitters "discovered" in some Canadian coins. From the moment I first read about it, the steamy stench of pasture patties loomed large in the air. I watched in amazement as the story grew and the apparent credibility so many "journalists" ascribed to it! Well, the United States Defense Security Service now admits that the statement is "unsubstantiated following an investigation into the matter."
My variation on the rule is this: if something is too stupid to be true, it absolutely is. And, of course, there's a corollary: media attention to silliness is inversely proporational to factuality.