What are some examples of irony in Catcher in the Rye?
Well, an overall ironic element is Holden's desire to preserve the innocence of the young. Yet while he goes about trying to accomplish this, he cannot help bringing corrupting influences into those lives. While trying to keep his little sister pure, he smokes, swears, drinks, runs away, and is needlessly and purposefully cruel to her. He is also very selective in who he thinks is worthy of this purifying effort. Jane Gallagher is meant to be protected because he believes her to be worthwhile and hates the idea of Stradlater making empty promises and aggressive sexual advances toward her. Yet, he carries out this same behavior with Sally.
He is stuck between the adult world and the world of children. When he is thrown into an adult situation, he acts like a child, as seen with Sunny, Carl Luce, etc. But when he retreats to the world of children, he brings his faux-adult act with him, as seen with Phoebe, or his fantasy destiny as the Catcher in the Rye.
It is fitting that his fascination with the ducks in Central Park occurs when he feels lost. The ducks innately know it is time to leave and where to go when the pond freezes and time changes. Holden's childhood pond is, like a museum, frozen, but he is shut out. Like his question about the ducks, he doesn't fly away; he is taken away by men in trucks, presumably wearing white jackets.