[Sic] of Bad Grammar?
If you know the difference between good and well, and that and which, then today is your (not you’re) day to unabashedly correct and edit bad grammar. *Finally!*
As a holiday, National Grammar Day is probably too (not to or two) new to have traditional celebrations, but at the minimum, I think it affords you the freedom to use proper English, and to help others do the same, without feeling like a hoity-toity grammar snob. Red pens ready!