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

Other days

self appreciation

Self Appreciation Day
ride the wind

Ride The Wind Day
martini

Martini Day
boba

Boba Day
fiancee

Fiancee Day
eat what you want

Eat What You Want Day
blanket fort

Blanket Fort Day
brow

Brow Day
lisp

Lisp Day
gum

Gum Day