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

Other days

blanket fort

Blanket Fort Day
kiss a brunette

Kiss A Brunette Day
comfy

Comfy Day
hoodie

Hoodie Day
one

One Day
book

Book Day
donate your hair

Donate Your Hair Day
boba

Boba Day
gum

Gum Day
lisp

Lisp Day