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

Other days

unicorn

Unicorn Day
hannah

Hannah Day
china

China Day
gum

Gum Day
self care

Self Care Day
law

Law Day
frozen yogurt

Frozen Yogurt Day
eat what you want

Eat What You Want Day
blanket fort

Blanket Fort Day
stud

Stud Day