In terms of "Vatican modern art" my favorite is the famous "Fire in the Borgo." In this painting from the 1500s, the pope is shown raising his popely hand from a safe distance and putting out a fire in a district of Rome. Every successive pope has been so eager to get in on the miracle-doing action that they have repainted their face on top of the prior pope's, so if you look at the painting from the side, the paint on the pope's face sticks out about an inch from the rest of the painting. Presumably Ben has got his little cameo up there by now.