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

Other days

tulip

Tulip Day
lisp

Lisp Day
kale

Kale Day
nae nae

Nae Nae Day
hiv awareness

Hiv Awareness Day
gallery

Gallery Day
get funky

Get Funky Day
cuddle up

Cuddle Up Day
lumpy rug

Lumpy Rug Day
ruby

Ruby Day