Oops, it doesn't look like 'flag upside down on day' is a national day..

Other days

buddy

Buddy Day
eat what you want

Eat What You Want Day
singles

Singles Day
reading

Reading Day
coffee

Coffee Day
brow

Brow Day
law

Law Day
lisp

Lisp Day
tell a fairytale

Tell A Fairytale Day
cat girl

Cat Girl Day