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

Other days

stud

Stud Day
promposal

Promposal Day
nail polish

Nail Polish Day
law

Law Day
my little pony

My Little Pony Day
lisp

Lisp Day
tulip

Tulip Day
camera

Camera Day
one

One Day
self appreciation

Self Appreciation Day