Kurt Vonnegut's 1969 novel Slaughterhouse-Five is steeped in irony. The subtitle of the book, after all, is "The Children's Crusade." He opens the novel by speaking in his own voice and the refrain is "so it goes," which is a brutal understatement of what he is writing about. It is a novel about World War II and his own experiences in the war, specifically the devastating firebombing of Dresden, Germany. By opening the novel in his own voice and discussing part of his writing process, he puts himself in the story, which is both playful and very postmodern. Certainly the ironic, black humor—and mix of fact and fiction—are very representative of the postmodern project.
Billy Pilgrim, the book's protagonist, is a decidedly ironic hero. Well, he's not a hero at all but rather a passive victim of a series of horrible events. This is exemplified when he becomes "unstuck in time." I think Vonnegut uses irony and dark humor to deal with what are very unpleasant subjects, such as war, violence, inhumanity, and cruelty. Vonnegut can't quite make sense of them so he filters them through these postmodern devices. To balance out the darkness of the subject matter, Vonnegut injects comic elements, puts himself into the narrative, and even brings in aliens, which undermines some of the seriousness of the book. Again, it's all very much in the spirit of postmodernism.