How Come Math Majors Are Always the Slowest to Understand This Concept?

Nerdy guy: I don't understand what the significance of the number 69 is. Can someone explain it to me?
Girl: You go to NYU and you don't know that?
(nerdy guy shakes his head)
Girl: To put it bluntly, it's two people giving each other head.
Nerdy guy: Wait, but what does that mean?
Girl: Oh my god...I can't tell you that now. You're the most innocent guy here. It would be like killing a unicorn.

--Kimmel Center, NYU