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

Other days

youth

Youth Day
tulip

Tulip Day
lumpy rug

Lumpy Rug Day
frozen yogurt

Frozen Yogurt Day
kiss a ginger

Kiss A Ginger Day
brow

Brow Day
cat girl

Cat Girl Day
kiss a brunette

Kiss A Brunette Day
offer

Offer Day
unicorn

Unicorn Day