While it is possible to compare examples of irony between Hawthorne's "The Birthmark" and O'Connor's "A Good man Is Hard to Find," the stories are really very dissimilar both in genre and content. In Hawthorne's, a good man seeks a spiritualized ideal and finds death in the loss of all he loves, while in O'Connor's, a petty and self-absorbed grandmother seeks Tennessee, gets Florida and finds death in the loss of all she loves, but in a very much more complicated way.
Aside from this overall description of seeking one thing and ironically getting its opposite and death, the easiest place to find similar ironies is in the climax and resolution of each story.
In Hawthorne's, Alymer succeeds in concocting a deep acting elixir to remove from Georgianna's cheek the red birthmark. She ironically trustingly drinks it, even though she has learned from reading his scientific journal that, ironically, when he expects success, he fails and when he succeeds, it is not according to expectation.
his most splendid successes were almost invariably failures, if compared with the ideal at which he aimed.
After drinking the elixir, Georgianna falls into a deep sleep. The red hand vanishes. Aminadab, who earlier ironically said, "If she were my wife, I'd never part with that birthmark," laughs a "gross, hoarse chuckle" of "delight" at what seems like success. Then Georgianna falls dead--and Aminadab ironically laughs again--after she speaks words releasing Alymer from blame:
Do not repent that with so high and pure a feeling, you have rejected the best the earth could offer. Aylmer, dearest Aylmer, I am dying!
Ironically, coarse and gross Aminadab values Georgianna rightly while "high and pure" Aylmer values only her spiritualized symbolic perfection, thus destroying her life.
In O'Connor's climax and resolution, The Misfit holds the grandmother at pistol point while his less than bright assistant Bobby Lee shoots "Bailey Boy" and his wife and two children farther out in the woods. After The Misfit exclaims that if he had been alive with Jesus, his life would not be what it is now, "if I had of been there I would of known and I wouldn't be like I am now," grandmother ironically has some sort of ill defined and ill described epiphany wherein she ironically seemingly recognizes The Misfit as one of her own children [Yet there is room for questioning ambiguity (or poor writing?) here: Is she delusional ("the old lady mumbled, not knowing what she was saying and feeling so dizzy") or does she somehow recognize a long lost child? If so, why does he spring "back as if a snake had bitten him": from hatred or pure rejection?]:
His voice seemed about to crack and the grandmother's head cleared for an instant. She saw the man's face twisted close to her own as if he were going to cry and she murmured, "Why you're one of my babies. You're one of my own children!"
The Misfit shoots her. Bobby Lee ironically remarks "Some fun!" implying inner laughter from an inferior assistant such as Aminadab was. The Misfit has already ironically said she would have been a good woman if, ironically, someone had continually shot her.
Ironically, the grandmother wanted more, including a visit to family, and she lost all, including her dearest family. The Misfit blames what he is on the godless age he lives in while ironically shooting someone who, at the very least, symbolizes his mother while ironically defining her goodness as needing to be shot a lot.