The most obvious example of irony in A Good Man is Hard to Find are words of the grandmother. The satire lies in the way she thinks about the world and what such reflections lead to. The woman thinks she is a good person, but her words and actions contradict to what she says.
Detailed answer:
The grandmother insists that when they move from Virginia to Florida, the family stop in Tennessee. On the roads, there is a fugitive criminal with his band, a maniac killer. They drive into a ditch, and then the killer appears. The grandmother recognizes him because she has seen the photo in the newspaper and tells him about it. It should not have been done. “You would all be better off if you didn’t recognize me,” he said. While his henchmen are taking the family into the forest, The Misfit talks privately with the grandmother.
The woman talks to the criminal as if he was a good and kind person. She ignores the fact that her family is being murdered at the same time. The grandmother helplessly tries to dissuade him from killing her relatives. She sees the killer as her son or persuades him about Jesus Christ. All the respectful thoughts, actions, and remarks of the grandmother lead to her family’s death. She cannot believe it until the very end, discouraging the killer. As a result, The Misfit breaks down and shoots the grandmother. The murder of all family members is a severe irony for all the plot lines.