According to Oversharers.com, an oversharer is “anyone who publicly shares embarrassingly intimate–or gross and disgusting–details of their lives, right out there where anyone can read them. On Facebook. On Twitter. On a blog. Or just about any other place on the web.”
My own personal favorite oversharer story involves a friend of a friend telling an entire party about her hymenectomy. But the ones on Oversharers.com are pretty great, too.