Glen's at it again. He started his talk on the "Economic Way of Thinking" with a discussion of why it's understandable that middle schoolers have, supposedly, gone hog wild for oral sex: they are substituting a lower cost form of sex for a higher cost one. Oral sex has a lower rate of STD transmission and a near-zero chance of pregnancy. If this is really happening, they are responding rationally to incentives.
Chris Martin is hanging in there though, especially since Glen has beautifully transitioned to the main ideas of his lecture.
It's worth noting that there's plenty of evidence to suggest that the stories of wild middle school oral sex orgies ("rainbow parties") are mostly urban legends.