My favourite story about the Sistine chapel relates to the wall fresco above the altar, The Last Judgment, which Michaelangelo also painted.
The fresco shows the final judgement of humanity, when souls are all sent to either heaven or hell.
The Vatican master of ceremonies Biagio da Cesena disliked the amount of nudity in the fresco and criticised Michaelangelo for it, also badmouthing him to the Pope. In response, Michaelangelo painted a likeness of Biagio da Cesena into the painting as King Minos in Hell - with donkey ears, naked, and with a snake biting him on the dick.
Cesena complained to the Pope, but the Pope brushed him off and told him basically "If it was Heaven I could maybe do something, but Hell isn't my area."