Oops, it doesn't look like 'office wore plaid on day' is a national day..

Other days

martini

Martini Day
boba

Boba Day
cuddle up

Cuddle Up Day
nae nae

Nae Nae Day
self appreciation

Self Appreciation Day
gum

Gum Day
ruby

Ruby Day
lisp

Lisp Day
self care

Self Care Day
me

Me Day