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

Other days

artists

Artists Day
fiancee

Fiancee Day
unicorn

Unicorn Day
nae nae

Nae Nae Day
lisp

Lisp Day
lash

Lash Day
eat what you want

Eat What You Want Day
tell a fairytale

Tell A Fairytale Day
kiss a ginger

Kiss A Ginger Day
boy friend

Boy Friend Day