Oops, it doesn't look like 'post your selfie with anthony joshua day' is a national day..

Other days

self care

Self Care Day
one

One Day
law

Law Day
slime

Slime Day
embarrass your best friend

Embarrass Your Best Friend Day
self appreciation

Self Appreciation Day
raise awerness of zeus

Raise Awerness Of Zeus Day
pampering

Pampering Day
blanket fort

Blanket Fort Day
boy friend

Boy Friend Day