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

Other days

youth

Youth Day
tell a fairytale

Tell A Fairytale Day
ruby

Ruby Day
polyamory

Polyamory Day
slime

Slime Day
boy friend

Boy Friend Day
cuddle up

Cuddle Up Day
fiancee

Fiancee Day
mean girls

Mean Girls Day
singles

Singles Day