Holden breaks the rules at Pencey by (a)sleeping in Ely´s bed; (b) staying out after curfew; (c) smoking.

(c) smoking

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.