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

Other days

boba

Boba Day
pick me

Pick Me Day
cuddle up

Cuddle Up Day
first love

First Love Day
china

China Day
frozen yogurt

Frozen Yogurt Day
one

One Day
bubble bath

Bubble Bath Day
polyamory

Polyamory Day
unicorn

Unicorn Day