In Geoffrey Chaucer's "The Pardoner's Tale," the pardoner's greed and dishonesty are excellent examples of situational irony. Situational irony occurs when someone does the opposite of what he is expected to do. In this instance, the pardoner is disrespectful and hypocritical while claiming to be a man of God.
The pardoner is an incredibly hypocritical man. He states that greediness is evil, but he then acts in a greedy manner. He sells pardons to people so that they can get into Heaven but keeps the money for himself instead of giving it to the church. One of the pardons he sells is even explicitly to absolve the sin of materialism. He is so full of greed that he also steals from the church collection basket. It is unusual for a man of the cloth to preach against a vice in which he takes part.
The pardoner is essentially a con man. He uses his talent for quick thinking to invent biblical stories and to convince people that they are doomed to go to Hell, causing the terrified parishioners to give him even more money. He admits to his fellow travelers that he wants to be rich and only preaches for money. Clearly the pardoner is not a holy man, no matter what he might claim to his victims.