International Talk Like a Pirate Day (ITLAPD) is a parodic holiday invented in 1995 by John Baur ("Ol' Chumbucket") and Mark Summers ("Cap'n Slappy"), of the United States, who proclaimed September 19 each year as the day when everyone in the world should talk like a pirate.
For example, an observer of this holiday would greet friends not with "Hello," but with "Ahoy, me haarrty!"
The date was selected because it was the birthday of Summers' ex-wife and consequently would be easy for him to remember. The holiday, and its observance, springs from a romanticized view of the Golden Age of Piracy. (— the preceding is from the Wikipedia article on International Talk Like a Pirate Day)