Irony is simply a difference between expectations and reality. For example, it’s ironic that a character defined by her bitterness, anger, and discontentment should be named “Joy.”
In Flannery O’Connor’s “Good Country People,” the eponymous group is highly praised by Joy’s mother and denigrated by Joy herself, who has renamed herself “Hulga” in an act of rebellion. Joy studied philosophy and believes herself to be higher-minded than those individuals she is surrounded with. She is especially put off by Mrs. Freeman’s obsession with discussing her daughters’ pregnancy or admirers. If she had a choice, Hulga would not live near any “good country people,” and instead have a job at a university to be surrounded by her fellow intellectuals.
Mrs. Hopewell, on the other hand, believes Joy (or Hulga’s) philosophy overcomplicates things; it is “simple,” hardworking people who are the most admirable. Consider Mrs. Hopewell’s assessment of Mrs. Freeman: she knew she was a nosy woman before she hired her and her husband, but hired them anyway because she was satisfied her expectations would be met. She knows the type of person Mrs. Freeman is, and therefore does not get any surprises. Good country people seems to mean simple, reliable, predictable, or straightforward.
This is why the plain talk of Manley Pointer appeals to Mrs. Hopewell. She sees him as a “salt of the earth” type, selling Bibles to make his living. He even says:
I’m real simple. I don’t know how to say a thing but to say it. I’m just a country boy.
He and Mrs. Hopewell connect over their praise of good country people. As Hulga later discovers, Pointer is not quite as predictable or salt of the earth as her mother previously thought, and turns out to be quite two-faced. This is the irony of the phrase. While Pointer does describe himself as good country people, maybe good country people are not as admirable as Mrs. Hopewell (who hopes well and sees the best in people) believes.