Although "A Good Man Is Hard to Find" begins with comedy, ultimately it shocks many readers. Did it shock you? Why or why not?
This is an answer that you yourself need to decide-were you shocked? I know that I was. You are right; it started off as kind-of funny. You have the whiney grandmother, the family vacation in the car, the pet cat...all fodder for some pretty funny situations. Even when the cat leaps, causing them to wreck, it is still mildly amusing. But then, as the car wrecks and The Misfit and his gang come onto the scene, the mood changes drastically. Family members are brought back into the woods. I was left feeling, okay, what is going on here? Are they REALLY taking them back there to kill them? I felt a bit betrayed, actually; I was reading along, really enjoying things, so I expected The Misfit to be another element of comedy somehow. But nope. It isn't. And then at the very end, as the grandmother finally shows a bit of softness, shows some vulnerability, the Misfit simply shoots her twice in the chest. Pretty shocking.
So, in the end, it did shock me, because it was so unapologetically violent. An old lady and her entire family just wiped out, shot to death. It is a complete surprise, considering the rather sardonic comedy routine that the story was up until that point. If I had been better prepared for it, if it had been grim before this point, or violent, the ending wouldn't have been so shocking. Anyway, those are just my thoughts; I hope they help to get your engines running a bit. Good luck!