Just to continue the above answer and offer you another example of irony and humor in Chaucer's The Prologue to the Canterbury Tales, the doctor is also presented with irony. The doctor is unmatched in, indeed, talk:
No one alive could talk as well as he did
On points of medicine and of surgery,...
And why can he talk so well about his profession? Because:
"...being grounded in astronomy,
He watched his patient's favorable star
and, by his Natural Magic, knew what are
The lucky hours and planetary degrees
For making charms and magic effigies.
Nothing qualifies a man for medicine and surgery like a knowledge of astrology and charm making! There is a fine line between irony and humor, and, in fact, surprise is the essence of both. In these few lines about the doctor, Chaucer achieves both.
Closely connected with the above is Chaucer's reference to the contemporary belief in the four humors and the horrible medicine the belief led to. The most common remedy for most illnesses was blood letting, thought to balance out the four fluids within the human body. Chaucer's juxtaposition of the doctor's love of astrology with his belief in the four humors and therefore blood letting may not be accidental.
Probably one of the best examples of irony in the General Prologue is in the description of most of the members of the clery, Parson excepted. Particularly look at the description of the Prioress. The Prioress is described as very lady-like and proper and she has a very tender heart when it comes to the treatment of animals. She is dressed very well and has superb manners. No where, however, does Chaucer indicate that she is pious and devout, as a nun in charge of a priory should be. That her outstanding qualities are not piety and devotion, but are good manners and sentimentality show great irony of character. The Friar is another good example of a member of the clergy with misplaced devotion. It seems his devotion is to himself and having a good time. We're told he extorts money from people in return for absolution and that he knows women and the inside of bars better than he knows the inside of a church. This time the greater emphasis is on the more humorous qualities of the Friar rather than on his other qualities. Whereas the Prioress seems to want people to think she is very devout, we get the impression that the Friar doesn't really care if people question his devotion to God. He's just enjoying his position and what he can get from it.