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

Other days

kale

Kale Day
youth

Youth Day
promposal

Promposal Day
bonang

Bonang Day
self care

Self Care Day
bow tie

Bow Tie Day
lash

Lash Day
nail polish

Nail Polish Day
aloxolt

Aloxolt Day
comfy

Comfy Day