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

Other days

self appreciation

Self Appreciation Day
bounce

Bounce Day
kale

Kale Day
camera

Camera Day
polyamory

Polyamory Day
hot chocolate

Hot Chocolate Day
bubble bath

Bubble Bath Day
hoodie

Hoodie Day
bow tie

Bow Tie Day
reading

Reading Day