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

Other days

fiancee

Fiancee Day
offer

Offer Day
bow tie

Bow Tie Day
hoodie

Hoodie Day
gum

Gum Day
first love

First Love Day
buddy

Buddy Day
boy friend

Boy Friend Day
brow

Brow Day
cursing

Cursing Day