How does Salinger use clothing and physical appearance to develop Robert Ackley?

We never learn what Ackley wears, but we do learn about his physical appearance. He is tall and round-shouldered with pimples and mossy teeth. He cuts his nails in Holden's room, and Holden has to keep telling him not to get the nail clippings on the floor. Holden thinks of him as "peculiar."
Ackley's appearance reflects his awkwardness and his lack of social skills. He doesn't seem to be able to see himself as others see him. For example, he doesn't seem to realize he might get along better with people if he brushed his teeth. He also doesn't seem to realize that Holden doesn't want to talk to him when he barges into his room, even though Holden doesn't look up from his book and later puts his hunting cap over his eyes. Even when Ackley is "nosy," as Holden puts it, he lacks sensitivity in how to approach other people.
Ackley, a slob, resents Stradlater, who is able to present himself well even though Holden characterizes him as a "secret slob." Ackley seems to wish he could act like Stradlater while insisting he hates him.
Holden feels sorry for Ackley and recognizes that they are both outsiders, so he invites him to the movies. At the end of the novel, he remembers Ackley and says he misses him sometimes.

Robert Ackley, Holden Caulfield's next-door neighbor in his boarding school dorm, is described as having terrible hygiene. He is described as having terrible acne and foul teeth/breath. In one scene, he goes so far as to clip his toenails all over Holden's floor. Salinger uses Ackley's gross, unhygienic appearance and behavior, and Holden's disgust at these things, to comedic effect. That Ackley is so unappealing also serves to explain why Holden doesn't like him, doesn't want to be around him, and gets so annoyed when he comes into his room (often unannounced and uninvited).
Ackley is described as pompous and acts as though he believes himself to be better than Holden. This attitude does not match up to Ackley's physical appearance and lack of self-care. He acts high and mighty, but it's doubtful when he last took a shower.