The dreaded elevator speech (or, can a book be pitched in a very few words?)

In marketing, it's called the elevator speech. The scenario: you happen to find yourself on an elevator with the ideal target for pitching your idea/product/self (a venture capitalist, editor, hiring manager, or whomever). You have, perhaps, fifteen seconds till he or she gets to their floor and exits. What do you say? How do you get him or her to "take a meeting?"

For writers, there's an elevator-speech variant: when a prospective reader (at a con or bookstore signing, say, or just happening...