In the men's restroom, the narrator becomes fixated on a small crack above the urinal's handle. This seemingly insignificant detail leads him to ponder the idea of vanishing into that space, revealing a deeper sense of isolation. He contemplates that if he were to disappear, it is likely that nobody would even notice his absence.
This thought reflects the narrator's feelings of detachment and insignificance in the larger world. The realization that no one would care about his disappearance emphasizes a profound sense of loneliness and the emptiness he experiences in his life.