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

Other days

bow tie

Bow Tie Day
believe

Believe Day
healing

Healing Day
comfy

Comfy Day
boba

Boba Day
brow

Brow Day
eat what you want

Eat What You Want Day
pumpkin

Pumpkin Day
azonto is acceptable

Azonto Is Acceptable Day
bonang

Bonang Day