In her book, 'A good man is hard to find', Flannery O'Connor works with different linguistic tools to give the story a sense of dark humor. One of these tools, being the use of irony.
The first appearance of this technique is at the beginning of the book, when O'Connor explains the reason behind her grandmother getting dressed for a car ride. "In case of an accident, anyone seeing the dead on the highway would know at once that she was a lady."
The writer then keeps on building the story line around the judgment that the grandmother holds up to everyone she meets. After the car crash and the Misfit makes his appearance, O'Connor writes: ""Listen," the grandmother almost screamed, "I know you are a good man, you dont look a bit like you have common blood. I know you must come from nice people!.""
The irony in this is that the grandmother believes that she can properly asses people based on how they look or act, at first encounter, when in reality the Misfit is a sociopath that is measuring all of his actions to get what he desires.