Pooping on or against something that is holy. Considered to be a faux pas in most cultures.
"Dude! So William visited the Sistine chapel yesterday, but got arrested for defecrating on the altar! I'd bail him out, but there's no deal when crucifixion is involved."
"Yea, and defecratest thou not in the Holiest of Grails, lest ye be damned into eternity."