There are lots of “days” for lots of things now – pizza, brothers, books, parties, plants, etc, etc.
Some you might agree with, others you don’t know and might not even understand. But someone did when they created it, they had a reason for it and every time it comes around, they celebrate it with reckless love and abandon.
You don’t need a widely distributed calendar to mark your own day for your own thing, you can simply do it and know that it’s your day.
Whose going to stop you?