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

Other days

boba

Boba Day
bounce

Bounce Day
bow tie

Bow Tie Day
martini

Martini Day
nail polish

Nail Polish Day
lumpy rug

Lumpy Rug Day
fiancee

Fiancee Day
ask out your crush

Ask Out Your Crush Day
slime

Slime Day
china

China Day