MWESTWOOD brings up a very interesting point here. Does goodness only come from the acceptance of grace as a result of (violent) crisis before death? Or can goodness grow from a "natural" acceptance of grace? Does revelation have to be violent in O'Connor's fictional world?
We can certainly point to many stories that agree with the premise that the epiphany of grace is always the result of violence ("Everything that Rises Must Converge", "The River", etc.).
In "Everything that Rises..." we have an example of a character, Julian, who receives his epiphany and lives. The epiphany is the result of violence, but he has the chance to change and to become a good man as he is allowed to go on living after his mother dies.
Perhaps then a "good man" is one that has been shown his own folly, his mistakes and hypocrisy, and has learned to accept these things as flaws instead of touting them as trophies.
Aside from the premise of the story, since you asked for our opinion, I would say that a GOOD man, whether it is a husband, friend, father, grandfather, or even co-worker, is an individual who is willing to put his own preferences and wants aside in order to serve others, help others, or motivate others to give the best they can give.
An example of a good man would be a father who sacrifices or works hard for the sake of his children. A father who would take his fun time to actually sit down and do homework with his children, who would give them advice, ensure that his kids feel loved, and that is responsible enough to provide as much as he can for their benefit.
Some people might have a picture of a good man as a fun-loving person, as a loyal husband, as a courageous military service member, as an inspiring teacher, but to me the best way a man can show his true goodness is through his treatment of his children, and that of his family.
In Flannery O'Connor's short story, "A Good Man is hard to Find," the Misfit tells the others, "Jesus thrown everything off balance." For, with Jesus came sentimentality, and with sentimentality a distortion of sentiment began with its emphasis upon the ordinary condition. This is the condition that the Misfit has been trying to resolve, and he cannot make punishment balance with a person's deeds:
"I call myself the Misfit...because i can't make what all I done wrong fit what all I gone through in punishment."
The Misfit finds that his faith is dead, for he finds no pleasure but in meanness, and in O'Connor's story he acts as an evil messenger from God (enotes). For others, such as the grandmother, grace comes at the moment of grisly death, at the point when the person has set aside her sentimentality. For O'Connor, a good man is hard to find because he is probably dead like the grandmother. If he were to live, he would have to endure the spiritual epiphany that he has had and be confronted, then, with the unbearable truth of a pathetic life, wasted in sentimentality.