A series of statistics describing the demographics of the male population at New York University. The Three-Thirds Rule states that one-third of the male population is gay, one-third is taken, and one-third is comprised of douchebags.
Chelsea: Hey, those three guys are totally hot!
Carla: Forget it, Chelsea. They go to NYU.
Chelsea: You think the three-thirds rule applies to them?
Carla: They're all wearing popped polo shirts and making out with each other when their girlfriends leave the room, so... yeah, I'm pretty sure.