Oops, it doesn't look like 'demi day' is a national day..

Other days

china

China Day
boba

Boba Day
brow

Brow Day
azonto is acceptable

Azonto Is Acceptable Day
blanket fort

Blanket Fort Day
my little pony

My Little Pony Day
lash

Lash Day
healing

Healing Day
lisp

Lisp Day
frozen yogurt

Frozen Yogurt Day