There's probably a clip of the full scene somewhere on Youtube. He essentially said, "What's the chance of a girl like me and a guy like you hooking up? [SIC]" And she said, "very small." And he says, "What are you talking, about, like one in a hundred?" and her response is, "More like one in a million." And he pauses, stares blankly at her for a couple seconds and then says, "So you're telling me there's a chance..."
I used this image a while back when someone took a screenshot of their attempts to use vanity gen to crack the 1Dky address. It gleefully listed his chances in scientific notation, and it reminded me of this scene in Dumb and Dumber, so I went out, found that image, and pasted it inside his screenshot.
Here's the post:
https://bitcointalk.org/index.php?topic=94675.msg1140956#msg1140956I'm not sure if this is the original use of it, I'm sure other people have had the same idea either before or since.