So... well... I just want to say I cursed Glenn Greenwald's writing because I was just reading his writing, and then I ran across him on video.
IN THE COMMENTS: People seem to figure out that the saying comes from Arabian folklore. And mcg quotes the Stephen Wright version:
"I cried because I had no shoes, 'till I met a man who had no feet. So I said, 'You got any shoes you're not using'?"
AND: From the new Bloggingheads with Bob Wright and Mickey Kaus:
BOB: Glenn Greenwald is on our site right now. Did you know that?
MICKEY: Oh, God, no. Really?
BOB: Hey, Mickey. It sounds like you want to challenge him to a duel.
MICKEY: I don't want to challenge anybody to a duel. You just... you'll let anybody in, won't you?
AND: Sorry I accidentally saved this as a draft after the update. I think Blogger just moved the buttons around today, and I didn't notice!