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

Other days

offer

Offer Day
first love

First Love Day
bow tie

Bow Tie Day
unicorn

Unicorn Day
prescription drug take back

Prescription Drug Take Back Day
tulip

Tulip Day
cuddle up

Cuddle Up Day
bounce

Bounce Day
slime

Slime Day
artists

Artists Day