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

Other days

kale

Kale Day
china

China Day
slime

Slime Day
promposal

Promposal Day
tell a fairytale

Tell A Fairytale Day
donate your hair

Donate Your Hair Day
blanket fort

Blanket Fort Day
polyamory

Polyamory Day
boba

Boba Day
ponytail

Ponytail Day