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

Other days

cursing

Cursing Day
prosecco

Prosecco Day
tulip

Tulip Day
lisp

Lisp Day
first love

First Love Day
ask out your crush

Ask Out Your Crush Day
pumpkin

Pumpkin Day
china

China Day
gum

Gum Day
self appreciation

Self Appreciation Day