Oops, it doesn't look like 'msm having a field day' is a national day..

Other days

slime

Slime Day
tulip

Tulip Day
kiss a ginger

Kiss A Ginger Day
cat girl

Cat Girl Day
ponytail

Ponytail Day
lisp

Lisp Day
ormille

Ormille Day
mean girls

Mean Girls Day
healing

Healing Day
boy friend

Boy Friend Day