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

Other days

book

Book Day
gum

Gum Day
lisp

Lisp Day
self care

Self Care Day
china

China Day
donate your hair

Donate Your Hair Day
pumpkin

Pumpkin Day
bow tie

Bow Tie Day
lumpy rug

Lumpy Rug Day
gallery

Gallery Day