One obvious way in which Holden shows disdain for rules is by smoking cigarettes in the dorm at school.
You weren't allowed to smoke in the dorm, but you could do it late at night when everybody was asleep or out and nobody could smell the smoke. Besides, I did it to annoy Stradlater. It drove him crazy when you broke any rules.
In explaining that he lit one cigarette in his room, he reveals that he was in the habit of doing it all the time.
Another more serious way in which Holden shows his disdain for rules is revealed in the fact that he had been expelled from school and was only hanging around for a few days before he would leave for good.
I wasn't supposed to come back after Christmas vacation, on account of I was flunking four subjects and not applying myself and all. . . . So I got the ax.
When he goes to say goodbye to Mr. Spencer, their conversation reveals that Pencey is not the first school that has expelled Holden for bad deportment. Mr. Spencer says:
"I believe you also had some difficulty at the Whooton School and at Elkton Hills."
Since Holden was only sixteen years old, he was undoubtedly showing disdain for rules by suddenly deciding not to wait for the term to end but to leave for New York City immediately. No doubt the school officials and his parents would be appalled to think of him wandering around Manhattan on his own for several days and nights, as he ended up doing in the novel.
In the city he goes into bars and orders drinks when he is deliberately breaking the law because he is too young to buy liquor and is tricking the establishments into breaking the law by serving it to him. For example, in Chapter 12 he shows that he has done a lot of drinking in addition to being addicted to cigarettes.
I ordered a Scotch and soca, which is my favorite drink, next to frozen Daiquiris.