a stomach can stretch upto 4 litres in capacity when pushed (one source). that's 4000cm³ (or 244 cubic inches).
to fill that capacity, the volume of a pizza needs to be 4000cm³ or 244 inch³.
take πr²h = 4000 for thin crust pizzas, if we assume the average height of pizza and toppings as 1cm, our equation simplifies to πr² = 4000; which gives the radius of the pizza as around 36 cms -- or a diameter of 72 cms (or 28").
if we take a thicker pizza of an average crust thickness of 1", then our equation for square inches simplifies to πr² = 244. which gives us a radius of about 9" or a diameter of 18".
since most pizzas top out at 12"-14" diameter (thin and thick crust volume varying between 700cm³ to 2600cm³), if anything, we're nowhere near achieving our full potential!
it may be that you were being facetious, but numbers and formulae are usually the most potent weapons in the arsenal of people who want to bulldoze in their own agenda.
as a general rule, any post with figures should warrant greater scrutiny, not less; and definitely not none with a nudge to rank it higher. even if it is one in all frivolity as my comment above.
Mythbusters once claimed that you couldn't die from drinking mentos and coke when they tests a pig stomach's capacity, oh man did that thing stretch like crazy, but they failed to account for flow from stomach into lungs while overfilling. In fact, merely a few liters could potentially prove fatal to a small untrained frame, such as those who died from the milk jug challenge.