What is it? Why does it exist? How? why? How? Why?
To understand why this day exists you'll need to take a trip back in time to the mid 80's and a Radio 4 program called The Million Pound Radio Show. Andy Hamilton and Nick Revell who were the main writers on this show kept up the same frenetic pace as had been achieved on television with Not The Nine O'Clock News. The show mainly covered similar sorts of topics and became famous in a set of bizarre circumstances.
British Airways in the early 1990's had procured thousands of episodes of Radio 4 comedies for use on its long-haul flights. Almost ironically, the Million Pound Radio Show had more listeners in this captured market than it did on the originaly playing on Radio 4.
Thanks to an unassuming and fairly typical sketch about a band of mutinous pirates who demand a Training Day to be set for September 19 (pressing their captain for the chance to "compare work methods and prioritise objectives, damn your eyes!") A number of people who heard this in the air, apparently telephoned the BBC to say this was the funniest thing they’d heard for years, and the sketch was repeated on a compilation CD highlighting the best moments of 1980’s programming.
Incedentally the Million Pound Radio Show is still played on BBC7 which has become a home for classic comedy, and not surprisingly today's episode contains the sketch which thousands alude to but very few actually know.