Holden is a terrible main character because he always lies and doesn't get along with almost all of the minor characters. His relationships with Stradlater, Mrs. Marrow, and Faith Cavendish especially prove his own deception and his own phoniness. In other words, he just doesn't get along with anyone, he lives for no reason, and he thinks everyone is phony except for himself.
Through Holden's relationship with Stradlater, it's easy to see why they don't get along. Holden thinks that Stradlater's a moron. One reason for this is Holden thinks that Stradlater doesn't respect Jane. Jane is one of Holden's best friends from childhood and Stradlater would rather give her the time and forget about her. That's why they both got into a fistfight. Also, while Stradlater is in the mirror combing his hair, Holden thinks about how much of a moron and a bastard he is. It seems that Holden just thinks this and doesn't have much real evidence. Holden tries to be friends with him and maintain a good relationship, but because Stradlater doesn't like the composition, and has no respect for Jane, Holden leaves forever.
Holden's relationship with Mrs. Marrow on the train shows his own personal deception and phoniness especially when he talks about her son. First, he lies about his name, injury, and why he's leaving Pency; which shows his general deception towards people. He distorts the real truth in his eyes about her son as well. This could mean that he really doesn't like her or he just doesn't like her son even though he doesn't really know him at all. He even goes so far as to think that Mrs. Marrow is a phony because she doesn't know the real truth about her son. Holden doesn't know the real truth either and because he lies about every detail about himself, he ends up being even phonier and more of a moron than her.
Holden shows a lot of deception and phoniness towards Faith Cavendish as well. Holden uses her, trying to make her go out with him at midnight, saying that he is only available that night.