Oops, it doesn't look like 'Only Child Self Awareness day' is a national day..

Other days

pick me

Pick Me Day
gum

Gum Day
polyamory

Polyamory Day
ruby

Ruby Day
coffee

Coffee Day
buddy

Buddy Day
cuddle up

Cuddle Up Day
slime

Slime Day
comfy

Comfy Day
martini

Martini Day