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

Other days

fiancee

Fiancee Day
china

China Day
eat what you want

Eat What You Want Day
kale

Kale Day
artists

Artists Day
hannah

Hannah Day
slime

Slime Day
prosecco

Prosecco Day
lisp

Lisp Day
coffee

Coffee Day