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

Other days

martini

Martini Day
bow tie

Bow Tie Day
polyamory

Polyamory Day
believe

Believe Day
boyfriend

Boyfriend Day
blanket fort

Blanket Fort Day
china

China Day
kale

Kale Day
kiss a ginger

Kiss A Ginger Day
offer

Offer Day