It's unclear where/when the tradition of National Pizza Day started. It's possible it was just made up last year by OC Foodies

October is National Pizza Month and there is information concerning how that started .

There is also National Cheese Pizza Day on Sept. 5, and National Sausage Pizza Day on Oct. 11 and National Pizza With Everything Day on Nov. 12, according to this article which is taken from the above OC Foodie source, which doesn't list why their dates are associated with the particular food items.

The cheese and sausage days do kinda sound like some sick joke, knowing about the alleged pizza code for girl and boy.

Rule 1

It's like a bad movie