Oops, it doesn't look like 'Lets Be Dick day' is a national day..

Other days

lisp

Lisp Day
slime

Slime Day
artists

Artists Day
unicorn

Unicorn Day
tulip

Tulip Day
blanket fort

Blanket Fort Day
bounce

Bounce Day
buddy

Buddy Day
cuddle up

Cuddle Up Day
believe

Believe Day