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

Other days

prosecco

Prosecco Day
promposal

Promposal Day
boyfriend

Boyfriend Day
camera

Camera Day
nail polish

Nail Polish Day
gum

Gum Day
unicorn

Unicorn Day
girl friend

Girl Friend Day
cat girl

Cat Girl Day
boy friend

Boy Friend Day