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

Other days

prosecco

Prosecco Day
lisp

Lisp Day
self care

Self Care Day
hoodie

Hoodie Day
one

One Day
singles

Singles Day
law

Law Day
artists

Artists Day
tell ur crush you like them

Tell Ur Crush You Like Them Day
cuddle up

Cuddle Up Day