I thought you had made that up! Heeee! If only I were that clever :) Nope, it's real day, but probably not that well-known in Europe, like most people here have probably never heard of Bastille Day or Walpurgisnacht. I first encountered Cinco de Mayo when I went to college in Texas (far too many years ago), but with the growth of the Latino population in the U.S., it's fast becoming a more mainstream holiday.