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

Other days

bounce

Bounce Day
bow tie

Bow Tie Day
girl friend

Girl Friend Day
prosecco

Prosecco Day
lash

Lash Day
pampering

Pampering Day
ormille

Ormille Day
artists

Artists Day
lumpy rug

Lumpy Rug Day
ruby

Ruby Day