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

Other days

ponytail

Ponytail Day
prosecco

Prosecco Day
buddy

Buddy Day
bow tie

Bow Tie Day
stud

Stud Day
china

China Day
brow

Brow Day
first love

First Love Day
my little pony

My Little Pony Day
singles

Singles Day