This oldie but goodie from 2008 surfaced on the website Reddit recently. It's a video of a 54-inch square Sicilian-style pizza being made and cooked. The folks at the appropriately named Big Mama's and Papa's Pizzeria in L.A. made this thing in an attempt to set a Guinness World Record for largest deliverable pizza. The pizzeria still makes the 54-inch pie. It's $199 plus tax and requires a 24-hour heads-up.
Says one Redditor:
I came on here to say that we ordered this for a party once and had to turn it sideways to get it in the door. And the toppings slid all over the place. Also we had to put it on the floor. We should have just ordered a bunch of smaller pizzas. It was pretty fun, though.
I suppose you'd sort of be limited to ordering it for picnics or for gatherings at places that had doorways with a span of more than 54 inches.