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

Other days

boy friend

Boy Friend Day
slime

Slime Day
mean girls

Mean Girls Day
gum

Gum Day
law

Law Day
lisp

Lisp Day
lost sock memorial

Lost Sock Memorial Day
girl friend

Girl Friend Day
buddy

Buddy Day
frozen yogurt

Frozen Yogurt Day