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

Other days

promposal

Promposal Day
hot chocolate

Hot Chocolate Day
stud

Stud Day
artists

Artists Day
china

China Day
latina equal pay

Latina Equal Pay Day
slime

Slime Day
my little pony

My Little Pony Day
cuddle up

Cuddle Up Day
tulip

Tulip Day