Holden constantly encounters people and situations that strike him as "phony," a word he applies to anything hypocritical, shallow, superficial, inauthentic, or otherwise fake. He sees such "phoniness" everywhere in the adult world, and believes adults are so phony that they can't even see their own phoniness. And Holden is right. Many of the characters in the novel, from Ackley and Stradlater, to Sally, to Mr. Spencer are often phony, and say and do things that keep up appearances rather than reflect what they truly think and feel.
Yet even though Holden is right that people are phony, Catcher in the Rye makes it clear that Holden's hatred of phoniness is still self-destructive. Though Holden is constantly pointing out the phoniness in others, he is himself often phony. At various times in the novel, he tells pointless lies, claims to like or agree with statements or ideas he hates, goes out with girls he doesn't like, all to try to feel less lonely or to avoid direct confrontations. The point, then, is that, yes, people are "phony" and can't live up to Holden's wish that the world be simple, a place of black and white. But in the end what Mr. Antolini is trying to make Holden see is that while this "phoniness" is harmful and hurtful, it doesn't make people evil or worthy of hate. It makes them human. Holden, in effect, is wishing that the world could be inhuman, could be something that it never can be.
From the very first scene of Catcher in the Rye, when Holden decides not to attend the football game that the rest of his school is attending, it is clear that Holden doesn't fit in. What makes The Catcher in the Rye unique, however, is not the fact that Holden is an alienated teenager, but its extremely accurate and nuanced portrayal of the causes, benefits, and costs of his isolation.
In short, alienation both protects and harms Holden. It protects him by ensuring that he will not ever have to form connections with other people that might wind up causing awkwardness, rejection, or the sort of intense emotional pain he felt when Allie died. Just as Holden wears his hunting cap as a sign of independence, separation, and protection from the world, he creates his own alienation for the same purpose. The problem, though, is that Holden is human. He may wish that he didn't need human contact, but he does. So while his alienation protects him, it also severely harms him, making him intensely lonely and depressed. He therefore reaches out, to Mr. Spencer, or Carl Luce, or Sally, but then his fear of human interaction reasserts itself and he does his best to insult or make the very people he wants to connect with angry at him. Holden has gotten himself caught in a cycle of self-destruction: his fear of human contact leads to alienation, which leads to loneliness, which causes him to reach out to another person, which excites his fear of human contact and leads to a terrible experience that convinces him that people are no good, which leads to alienation… and so on.
Like most teenagers, Holden struggles with his sexuality. He considers himself a "sex maniac," but is also completely inexperienced. In addition, he has very strong and often contradictory feelings about women. Most women, such as Bernice Krebs and Sally Hayes, he sees as utterly stupid, largely because they seem interested in boys and men, whom Holden knows from experience are up to no good. On the other hand, Holden sees Jane Gallagher as a perfect woman: kind, loving, gentle, innocent, wonderful. In other words, he idealizes her. Yet the fact that he is so frightened to call or talk to her implies that he knows that she can't possibly be as perfect as he wants her to be. In the end, Holden's feelings about women and sex mirror his feelings about society as a whole. He desperately wants to have a girlfriend, have sex, and achieve emotional intimacy, and at the same time is desperately afraid as well.
In contrast to all adults whom Holden sees as riddled with flaws and phoniness, he sees children as pure, gentle, innocent, and perfect. The characters he speaks most fondly about in the novel are all children: Allie, Phoebe, and the poor boy he hears singing the song about the "catcher in the rye." He constantly dreams up schemes to escape growing up, such as fleeing to a New England cabin or working on a ranch out West. The only role that Holden envisions for himself in life—catching children before they fall off a cliff—is symbolic of his wish to save himself and other children from having to one day grow up.
However, Holden's view of perfect childhood is as incorrect as his view of the adult world as entirely "phony," and just helps Holden hide from the fact that the complex issues ranging from sex, to intimacy, to facing death, all of which he will have to face in growing up, terrify him. Further, this form of delusional self-protection can only last so long. Holden will grow up, whether he likes it or not. Mr. Antolini and Phoebe both make it clear that unless he learns to accept the complexities of adulthood, he will end up, at best, bitter and alone.
If "phony" is the most frequently repeated word in The Catcher in the Rye, "crazy," "madman," and "depressed" rank close behind it. Because Holden is the narrator of the novel, and because he seems in so many ways to be a typical teenager battling typical teenage issues of identity, it seems like he is using these words for effect. In other words, when he says he's crazy he seems to mean that he's acting oddly, or inconsistently, or stupidly, but not that he's actually going insane. And when he says he wishes he were dead, it likewise seems at first as if he's using the phrase as a teenage expression to make his emotions seem as intense to you as they seem to him. But as the novel progresses, it begins to become clear through hints and an intensification of Holden's own language that Holden really is on the verge of losing it, and really is seriously thinking of killing himself as the only way out of this world he can't control or understand.