Mainly remembered for getting in an argument with the fool, the friar is the opposite of the Cardinal. While the Cardinal represents a figure of Catholic authority who makes the Christian life completely define his personality, the friar represents someone who does the opposite. He first laughs at religious officials who he should probably be defending and then gets all angry when someone (the fool) attacks friars specifically.
"But a certain friar, graduate in divinity, found such pleasure in this jest at the expensive of priests and monks that he too began to make merry, though generally he was grave to the point of sourness." (1.26)
Once he's angry, he can't even defend himself because he's too personally insulted to make an actual argument. Instead of communicating tranquility, patience, and all those other good holy qualities, he freaks out and says mean, nasty insults and behaves in a generally un-Christian way. Not unlike the lawyer, this guy also wants to make you move to Utopia.