Holden’s rule about sex is that he is not going to mess around with girls that irritate him, but he has trouble sticking to his rules.
Like most teenage boys, Holden does not understand sex. He gets frustrated because he can’t seem to stick to his principles and morals. He does not want to associate with phonies, for example. Holden tries to protect himself from self-loathing by making rules.
Last year I made a rule that I was going to quit horsing around with girls that, deep down, gave me a pain in the ass. (ch 9)
Holden broke the rule within a week. He realized that he did not understand girls, or sex. He spends time with “crumby” girls, in a “crumby” way, and is unable to respect himself or other girls. Sex is just another aspect of life with which Holden feels uncomfortable and inadequate.