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

Other days

stud

Stud Day
bow tie

Bow Tie Day
tulip

Tulip Day
pick me

Pick Me Day
get funky

Get Funky Day
self appreciation

Self Appreciation Day
emoji

Emoji Day
offer

Offer Day
tell a fairytale

Tell A Fairytale Day
my little pony

My Little Pony Day