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

Other days

gum

Gum Day
cursing

Cursing Day
cat girl

Cat Girl Day
first love

First Love Day
kale

Kale Day
cuddle up

Cuddle Up Day
hoodie

Hoodie Day
pampering

Pampering Day
nae nae

Nae Nae Day
boyfriend

Boyfriend Day