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

Other days

martini

Martini Day
kiss a brunette

Kiss A Brunette Day
stud

Stud Day
girl friend

Girl Friend Day
gum

Gum Day
first love

First Love Day
brow

Brow Day
hot chocolate

Hot Chocolate Day
lisp

Lisp Day
boba

Boba Day