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

Other days

frozen yogurt

Frozen Yogurt Day
martini

Martini Day
boba

Boba Day
singles

Singles Day
bow tie

Bow Tie Day
china

China Day
ask out your crush

Ask Out Your Crush Day
bounce

Bounce Day
nae nae

Nae Nae Day
self appreciation

Self Appreciation Day