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

Other days

bow tie

Bow Tie Day
slime

Slime Day
self care

Self Care Day
donate your hair

Donate Your Hair Day
boba

Boba Day
polyamory

Polyamory Day
blanket fort

Blanket Fort Day
nail polish

Nail Polish Day
tulip

Tulip Day
one

One Day