For the worst pizza in Rome, you have to start from the Piazza San Pietro. Face the Basilica, and take the exit from the piazza to your right, fighting your way through crowds of alabastor Americans, as if you were going around to the entrance to the Vatican Museums. At the traffic lights, turn right. The second pizzeria on the right is the one you are looking for. It's called The Swiss Guard, after the clowns who guard His Holiness.
Observe the local customs of creating pizza. Firstly, the base must be thin and dry, and slightly burnt on the bottom. In contrast, the upper surface of the base must be uncooked and as slushy as freshly defouled snow. The tomato sauce must be painfully sweet, denoting its transubstantiation from a powder. The mozzarella must be melted, yet carefully unbrowned - this would add flavour. The prosciutto must have the unhealthy pinkness of a freshly picked scab. No herbs, no pepper, and certainly no salt are added; this would completely ruin the desired sensation of eating medium density fiberboard. Considering that I travelled to Rome primarily because of its reputation for culinary excellence, I must say I was slightly disappointed. The holiday got worse from that point.