Oops, it doesn't look like 'U Post Pics W Them day' is a national day..

Other days

bow tie

Bow Tie Day
lumpy rug

Lumpy Rug Day
polyamory

Polyamory Day
unicorn

Unicorn Day
kiss a brunette

Kiss A Brunette Day
book

Book Day
law

Law Day
slime

Slime Day
pick me

Pick Me Day
first love

First Love Day