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

Other days

hoodie

Hoodie Day
kiss a brunette

Kiss A Brunette Day
first love

First Love Day
stud

Stud Day
prosecco

Prosecco Day
blanket fort

Blanket Fort Day
china

China Day
law

Law Day
nae nae

Nae Nae Day
bow tie

Bow Tie Day