A Good Man Is Hard to Find is the tale of an average family vacation gone awry. Waaayyy awry. As in, the family winds up dead in the end. It's not exactly uplifting, and these characters aren't exactly likable. Nonetheless, we think your students will be able to relate.
Whether or not they've ever had to spend hours on end confined in a car with a self-righteous, manipulative relative like the grandmother of A Good Man, they'll probably recognize some of the passive-aggressive behaviors she employs. Who hasn't been guilt-tripped into doing something at some point in their lives? By a relative, by a friend, it doesn't matter. When your students witness the behavior of the grandmother, it will stir their passions. Sure, they might hate her, but that's okay. Emotion equals engagement, and you can work with that.