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

Other days

donate your hair

Donate Your Hair Day
unicorn

Unicorn Day
ruby

Ruby Day
bow tie

Bow Tie Day
gum

Gum Day
lash

Lash Day
hoodie

Hoodie Day
hiv awareness

Hiv Awareness Day
nail polish

Nail Polish Day
buddy

Buddy Day