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

Other days

get funky

Get Funky Day
hannah

Hannah Day
unicorn

Unicorn Day
polyamory

Polyamory Day
my little pony

My Little Pony Day
lisp

Lisp Day
first love

First Love Day
coffee

Coffee Day
bow tie

Bow Tie Day
lumpy rug

Lumpy Rug Day