The latest xkcd, and especially the mouseover text, reminds me of my longtime curiosity about the phenomenon of slash fiction. It's male/male erotica, usually taking the form of short stories about characters from sci-fi or fantasy written by heterosexual women. The term 'slash' comes from the punctuation used when categorizing the stories by the protagonists' names -- Kirk/Spock, Angel/Xander, Remus/Sirius, or whatever. I guess you could see the popularity of Brokeback Mountain as springing from the same forces that make slash popular.
What I find interesting about slash is that it's a sort of sexual expression that wasn't promoted by the usual social forces shaping people's sexual desires. Nobody was out there trying to get women interested in gay sex between Kirk and Spock, in the same way that a variety of social forces were telling them to be chaste until they married some tall guy with a steady job, and then bear his two sons and a daughter. And it wasn't that they were just writing fanfic about themselves and Kirk or Spock, which would be a rather straightforward expression of the innate desires you'd expect. The way we usually understand the biological and social forces involved push against this happening, and yet it happens!
Girls are interesting and I want to know more about them.