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

Other days

gum

Gum Day
artists

Artists Day
buddy

Buddy Day
chocolate milkshake

Chocolate Milkshake Day
nae nae

Nae Nae Day
book

Book Day
ruby

Ruby Day
pick me

Pick Me Day
eat what you want

Eat What You Want Day
slime

Slime Day