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

Other days

martini

Martini Day
stud

Stud Day
stress awareness

Stress Awareness Day
law

Law Day
first love

First Love Day
lisp

Lisp Day
ride the wind

Ride The Wind Day
nae nae

Nae Nae Day
brow

Brow Day
healing

Healing Day