On March 10th, we celebrate Ninternational Mario Day. This is a day where you can get those last few star coins in NSMBU, race your buddies on Mario Kart 7, or make Mario a huge cake, for no real reason.
Really there's not a big reason for celebrating, except March 10th can be written as MAR10, which looks like MARIO.
(No I wasn't the guy who wrote the letter about it and got featured u-u).