If you've been seeing lots of images of a certain Italian plumber all day, there's a reason: It's Mario Day, kind of like the gamers' version of May 4 for Star Wars fans. Mario Day is celebrated on March 10, as in M-A-R-1-O, notes Variety. As Mariowiki recounts, fan invented the day about a decade ago, but since then it has been fully embraced by both Nintendo and retailers that sell Mario goods.