Your Fly is Open

"The skeptic is never for real. There he stands, cocktail in hand, left arm draped languorously on one end of the mantelpiece, telling you that he can't be sure of anything, not even of his own existence. I'll give you my secret method of demolishing universal skepticism in four words. Whisper to him: "Your fly is open." If he thinks knowledge is so all-fired impossible, why does he always look?" 

--Robert Farrar Capon, Hunting the Divine Fox (1974 A.D.), quoted in James Sire, The Universe Next Door (2009 A.D.)