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

Other days

ruby

Ruby Day
first love

First Love Day
slime

Slime Day
tell a fairytale

Tell A Fairytale Day
china

China Day
ormille

Ormille Day
gum

Gum Day
book

Book Day
coffee

Coffee Day
kiss a ginger

Kiss A Ginger Day