For me it was a first name (unusual) and two schools attended (this in the days when universities were much more liberal with posting their student directories.

Let's face it, at most one if your identities can be tied to your actual real-world activities. Otherwise people can find enough correlations to out you. Witness JK Rowling's new book.

JK Rowling's dox was a result of a member of the publishing house's solicitors telling his wife, who then told a close friend who provided the initial leak on twitter, which gave the newspaper breaking the story enough to go on to start drawing those conclusions.

Found the BBC story about this, if you're interested. http://www.bbc.co.uk/news/entertainment-arts-23366660

Meh, you lot will never figure out my real world identity!

If only I knew your phone number ...

I would have gotten away with it, if it weren't for you meddling kids!