"MadHatterDay is a holiday in October. It fills the need for a second crazy day in the year, almost exactly half a year from April Fools' Day. The real spirit of MadHatterDay is turnabout: The nonsense we usually have to pretend is sane can be called madness for one day in the year; the superficially crazy things that really make sense can be called sane on MadHatterDay.
MadHatterDay is 10/6. The date was chosen from the illustrations by John Tenniel in Alice's Adventures in Wonderland, wherein the Mad Hatter is always seen wearing a hat bearing a slip of paper with the notation "In this style 10/6". We take this as inspiration to behave in the style of the Mad Hatter on 10/6 (which is October 6 here, although in Britain MadHatterDay occurs on June 10.)
MadHatterDay began in Boulder, CO, in 1986, among some computer folk who had nothing better to do. It was immediately recognized as valuable because they caused less damage than if they'd been doing their jobs. It was announced that first year on computer networks. In 1987 it gained minor local recognition. In 1988, it was first recognized as an official holiday by an area business, and also received its first national press coverage by news services (who are always desperate for an unlikely story). It is almost certain that the national election also gave MadHatterDay a good boost in 1988.
Reproduced from Ari Rapkin's Mad Hatter page http://www.cs.cmu.edu/~ari/madHatter.html