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

Other days

stud

Stud Day
bow tie

Bow Tie Day
cuddle up

Cuddle Up Day
hannah

Hannah Day
nae nae

Nae Nae Day
bounce

Bounce Day
mean girls

Mean Girls Day
slime

Slime Day
lash

Lash Day
reading

Reading Day