Near the book's climax, in Chapter 21, Vonnegut uses vivid visual imagery to describe the moment when Dwayne Hoover first sees Kilgore Trout:
But the brightest new light in the room by far was the bosom of Kilgore Trout's new evening shirt. Its brilliance twinkled and had depth. It might have been the top of a slumping, open sack of radioactive diamonds.
This quote is full of highly visual imagery like "twinkled," "diamonds," and "bright." This kind of imagery is rare for Vonnegut: often his style avoids elaborate sensory detail. Here, though, Vonnegut uses imagery to accentuate the difference between image and reality at a climactic moment in the novel.
This scene, in which Trout's evening shirt becomes suddenly florescent when the bar's UV lights are turned on, triggers Dwayne's madness: it's the florescent shirt that causes him to approach Trout and dig his chin into his shoulder, which causes Trout to give him the novel that convinces him he is the only person in the universe with free will. Vonnegut's imagery matches the way Dwayne's madness is set off by fiction because it describes Trout's shirt with imagery that would be apt for great wealth and beauty. In other words, the imagery outmatches the reality: "brilliance" and comparisons to "diamonds" are nearly absurd for the bosom of a shirt, even in florescent light. This matches the way Dwayne becomes enamored by a fiction.
Vonnegut's comparison of the shirt to "diamonds" is particularly relevant to the themes of consumerism and money that extend throughout the novel. By likening the trigger of Dwayne's madness to a form of wealth, Vonnegut gestures to the way money and riches are also often an aspirational fiction that causes people to lose sight of their real values. By reinforcing the entanglement between ideas and the material world, Vonnegut's imagery extends possible readings of Dwayne's madness to include critiques of contemporary consumerism.