Oops, it doesn't look like 'park on a hot summer day' is a national day..

Other days

slime

Slime Day
bow tie

Bow Tie Day
hannah

Hannah Day
ask out your crush

Ask Out Your Crush Day
martini

Martini Day
law

Law Day
gum

Gum Day
stud

Stud Day
nail polish

Nail Polish Day
gallery

Gallery Day