Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Angry, Fearful
Stephen Rojack is as angry as the Hulk and as crazy as the Joker—and that's one killer combo.
Every word is soaked in Rojack's overbearing anger. After killing Deborah, for example, he wonders if he "had been too gentle" and "had not plumbed the hatred where the real injustice was stored" (2.86). Like, he could've killed her a little harder or something sick like that. We see this anger bubble up again and again, whether Rojack's in a fistfight with Shago or a tense standoff with Barney Kelly. He is bitter about the way his life has turned out and expresses this disappointment through an endless stream of pretty heinous actions—his anger permeates the book.
Whenever he's not caught up in a righteous rage, however, Rojack is nothing more than a frightened and sad dude. He complains about how his "dread was real" and that "omens were as tangible as bread" (7.208). Later, at Kelly's apartment, he becomes overwhelmed by a "distillate of gloom" (8.8). If Mailer's goal was to place us inside the mind of a madman, then the alternately angry and frightened tone serves him well—we recognize Rojack as deeply wounded, while also fearing his rage.