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

Other days

buddy

Buddy Day
lisp

Lisp Day
nae nae

Nae Nae Day
martini

Martini Day
stud

Stud Day
bow tie

Bow Tie Day
gum

Gum Day
pumpkin

Pumpkin Day
mean girls

Mean Girls Day
eat what you want

Eat What You Want Day