As I'm sure we all know, Terry Pratchett is the genius writer of The Discworld series, many standalone novels and children's books and a hilarious co-written book with Neil Gaiman titled Good Omens as well as radio plays, television versions, graphic novel editions and even a GURPS roleplaying game. (If you didn't know, get thee to a library.) He's terrifically absurd, with an odd sense of humour (to say the least) and a clever use of footnotes.
Sadly, he was diagnosed with early onset Alzheimer's disease and though he himself claims to be taking it "fairly philosophically and with mild optimism", he's been fighting for more funding for Alzheimer's research and fans have taken up the cause. This has lead to:
Match it for Pratchett: Wear The Lilac
It is a tribute to the Terry Pratchett's writing skills and his friendly attitude to fans that he has inspired not only Match It For Pratchet but a second campaigns to raise money for Alzheimer's.
In Nightwatch, the men who fought and died (and in one case, fought, died and kept on fighting) in the Revolution are remembered by the wearing of sprigs of lilac every May 25th. The online Pratchett communities have adopted May 25th as Wear The Lilac day, an unofficial holiday celebrating Pratchett's work.
More info at: http://www.matchitforpratchett.org/, though the site is slightly outdated.
It honours the books, the writer and gives you a chance to go "!!!" at people, if you can pronounce that at least.
So pin a sprig of lilacs to your jacket or bring this and towel day together and wear a lilac towel, just don't forget to match it for Pratchett.