Inspired by the character of the Mad Hatter as depicted in Alice's Adventures in Wonderland, Mad Hatter Day (also frequently appearing without spaces, as "MadHatterDay") is a semi-official holiday created to be a "second Silly Day", bridging the gap between each occurrence of April Fool's Day. In the US, it falls on the sixth of October each year, due to illustrations where the Hatter's oversized hat is labeled "In this style 10/6"; it is considered an amusing coincidence that this date is almost a half year away from April Fool's Day. However, due to alternate systems of dating, in the UK it occurs on June tenth.
Originating in Boulder, Colorado, the holiday reportedly gained some local recognition during the late 1980s.
"Some astute observers have noted that the paper in the Mad Hatter's Hat was really an order to make a hat in the style shown, to cost ten shillings sixpence. However, it is well known that Time Is Money, and therefore Money Is Time, and therefore 10/6 may as well be the sixth of October."
Mad Hatter Day is one of numerous Discordian "Holydays" [sic].