The Dismal Science, in a couple of lines.
From the freakonomics people's nytimes interview with a couple of prostitutes (h/t: Amber):
Q: If men pay by the hour, they would want to consume as many acts per hour as possible. How do sex workers feel about this?
MINDY: I’m trying to be delicate with my answer: this usually doesn’t happen.
DOROTHY: Is he kidding?
(Noting that the question wasn't proffered by one of the freakonomics authors -- presumably they're not that stupid. But I'll bet it was proffered by someone who had just walked out of an undergraduate micro class... or read something of Gary Becker's.)