Random holidays:

  1. New Year's Day
    January 1
  2. Lunar New Year
    January/February
  3. Chinese New Year
    January/February
  4. Valentine's Day
    February 14
  5. Mardis Gras
    Saturday before Ash Wednesday
  6. Ash Wednesday
    46 days before Easter
  7. St. Patrick's Day
    March 17
  8. Passover
    March/April/May
  9. Good Friday
    March/April
  10. Easter
    March/April
  11. April Fool's Day
    April 1
  12. Songkran
    April 13-15
Randomizing…

Go ahead and laugh but some people take these random holidays seriously. I think, as long as you get the day off, who cares. Don't like these holidays? You could instead generate a random calendar date and make up your own holiday.