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

Other days

slime

Slime Day
kale

Kale Day
tulip

Tulip Day
boy friend

Boy Friend Day
pampering

Pampering Day
youth

Youth Day
unicorn

Unicorn Day
ride the wind

Ride The Wind Day
one

One Day
donate your hair

Donate Your Hair Day