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

Other days

stud

Stud Day
boba

Boba Day
pampering

Pampering Day
ormille

Ormille Day
youth

Youth Day
nae nae

Nae Nae Day
ride the wind

Ride The Wind Day
bubble bath

Bubble Bath Day
brow

Brow Day
one

One Day