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

Other days

slime

Slime Day
believe

Believe Day
bow tie

Bow Tie Day
stud

Stud Day
lost sock memorial

Lost Sock Memorial Day
mean girls

Mean Girls Day
ruby

Ruby Day
lisp

Lisp Day
frozen yogurt

Frozen Yogurt Day
promposal

Promposal Day