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

Other days

ruby

Ruby Day
book

Book Day
kiss a brunette

Kiss A Brunette Day
boyfriend

Boyfriend Day
mean girls

Mean Girls Day
lisp

Lisp Day
boy friend

Boy Friend Day
kiss a ginger

Kiss A Ginger Day
my little pony

My Little Pony Day
slime

Slime Day