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

Other days

one

One Day
bow tie

Bow Tie Day
pick me

Pick Me Day
healing

Healing Day
donate your hair

Donate Your Hair Day
ruby

Ruby Day
kale

Kale Day
law

Law Day
comfy

Comfy Day
ask out your crush

Ask Out Your Crush Day