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

Other days

one

One Day
youth

Youth Day
azonto is acceptable

Azonto Is Acceptable Day
frozen yogurt

Frozen Yogurt Day
gum

Gum Day
boyfriend

Boyfriend Day
eat what you want

Eat What You Want Day
lisp

Lisp Day
hannah

Hannah Day
book

Book Day