This post on LanguageLog has a number of facetious "Linguistically Noteworthy Dates in May," written by late linguist Jim McCawley. Some of them are just odd and have very little to do with linguistics itself--e.g., "The University of Chicago trades Leonard Bloomfield to Yale University for two janitors and an undisclosed number of concrete gargoyles." (Bloomfield was a famous linguist, but that's about the only ling. content as far as I can tell.)
Others, despite my Master's degree, I don't get at all. But I do get the following and find them rather cute. (Raise your hand if you understand them. I'm willing to explain them to the best of my ability, but you know what they say about the funniness of a joke once you have to explain it.)
- May 5, 1403. The Great English Vowel Shift begins. Giles of Tottenham calls for ale at his favorite pub and is perplexed when the barmaid tells him that the fishmonger is next door.
- May 11, 1032. Holy Roman Emperor Conrad II orders isoglosses erected across northern Germany as defense against Viking intruders.
- May 19. Diphthong Day. (Public holiday in Australia)
- May 20, 473 B.C. Publisher returns to Panini a manuscript entitled Saptadhyayi with a note requesting the addition of a chapter on phonology. Panini begins struggling to meet the publisher's deadline.
- May 29, 1962. Angular brackets are discovered. Classes at M.I.T. are dismissed and much Latvian plum brandy is consumed.
- May 30, 1939. Charles F. Hockett finishes composing the music for the Linguistic Society of America's anthem, 'Can You Hear the Difference?'
...and even with those, I don't get every aspect of them. Why Latvian plum brandy? I don't know. But I do know why angular brackets. (Though actually, square brackets would make more linguistically-celebratory sense.)