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

Other days

bow tie

Bow Tie Day
lash

Lash Day
nail polish

Nail Polish Day
stud

Stud Day
self care

Self Care Day
donate your hair

Donate Your Hair Day
pampering

Pampering Day
china

China Day
promposal

Promposal Day
lumpy rug

Lumpy Rug Day