Of course, I have a dirty mind, too, so it immediately came to mind that there should be a "sexster", which would consist of links between people you've slept with. This way you could figure out how many degrees-of-copulation separate you and . . . some number of other people. Okay, yes, it obviously wouldn't work at all, for privacy reasons. But you can imagine it, because it does actually exist, even if you can't see it. For instance, I've transitively (two steps!) had sex with Alastair, who I played golf with last weekend.
(This has been mocked (up) at std-ster . . . thanks to Kaihsu & (transitively!) Ken for the link)
The (slightly) more innocent original version of this was the hand-made charts of who had kissed/messed-around-with who, that used to get passed around at youth-group conventions I went to when I was a teen. Back then, I didn't make it onto the charts. :-) posted by Miles 3:39 PM