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

Other days

self care

Self Care Day
gum

Gum Day
ponytail

Ponytail Day
kale

Kale Day
hoodie

Hoodie Day
my little pony

My Little Pony Day
ormille

Ormille Day
bow tie

Bow Tie Day
lisp

Lisp Day
cat girl

Cat Girl Day