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

Other days

slime

Slime Day
kiss a brunette

Kiss A Brunette Day
singles

Singles Day
promposal

Promposal Day
lumpy rug

Lumpy Rug Day
bow tie

Bow Tie Day
kale

Kale Day
ruby

Ruby Day
eat what you want

Eat What You Want Day
artists

Artists Day