What is the origin of the idiom "holier than the Pope" and when to use it?

The origin of the idiom "holier than the Pope" is not well-documented, but it likely evolved from the concept of religious piety and the comparison of one's perceived moral superiority to that of the Pope, who is considered the highest authority in the Roman Catholic Church. It is used to describe someone who acts or presents themselves as morally superior, excessively pious, or self-righteous, often to the point of being hypocritical or judgmental of others.