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

Other days

ruby

Ruby Day
brow

Brow Day
coffee

Coffee Day
martini

Martini Day
eat what you want

Eat What You Want Day
slime

Slime Day
healing

Healing Day
tell ur crush you like them

Tell Ur Crush You Like Them Day
comfy

Comfy Day
one

One Day