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

Other days

tulip

Tulip Day
singles

Singles Day
bounce

Bounce Day
gum

Gum Day
blanket fort

Blanket Fort Day
buddy

Buddy Day
bow tie

Bow Tie Day
kiss a brunette

Kiss A Brunette Day
china

China Day
ponytail

Ponytail Day