To all of the bored data scientists who are looking for interesting demo. (Alternatively, to all the startups who want to do a fraud detection demo). I stumbled upon this weird dataset which was part of PAN 2012 conference: identifying sexual predators in chat rooms.
A less bizarre dataset is the beer classification dataset reported in William M. Briggs blog. It is the classical geeky cool dataset since it shows you are a data scientist who likes beer.
Additional borderline dataset is how clean are SF restaurants dataset I wrote about before.