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

Other days

cursing

Cursing Day
ponytail

Ponytail Day
pick me

Pick Me Day
ormille

Ormille Day
hannah

Hannah Day
boy friend

Boy Friend Day
chocolate milkshake

Chocolate Milkshake Day
girl friend

Girl Friend Day
artists

Artists Day
lisp

Lisp Day