Beginning in chapter one and throughout the novel, Holden tends to dismiss many important details with throwaway phrases like “this madman stuff.” Why does Holden skim over parts of his narrative in this way?
This is Holden's way of downplaying things that bother him. By speaking in casual abstractions, he creates a facade for himself that makes him seem untroubled.
Holden doesn't have much facility with language and is not articulate enough to relate his story in a more precise way.
As an unreliable narrator, Holden leaves out information purposefully to mislead and confuse the reader.
It is likely that Holden is experiencing memory problems due to his nervous breakdown; he expresses his desire to communicate in greater detail and appears to be frustrated that he cannot offer better descriptions of events that happened to him.
Holden reveals that he is embarrassed and ashamed of his situation, which is probably the reason why he glosses over many details of his experience.