What is disturbing to Holden about a nun teaching English? What depresses him about them?

The nuns, in addition to being nuns, are schoolteachers from Chicago who have just come to New York. One of the nuns teaches English, and Holden wonders how she feels about the sexy bits of books she has to teach. You know, since she’s a nun. So they start talking about English (Holden’s best subject), and we get a nice list of the books he’s read: Beowulf, Lord Randal My Son, Return of the Native, Romeo and Juliet, etc. The nun gets all excited about Romeo and Juliet, which Holden thinks isn’t exactly nun-appropriate. But he indulges in a discussion of it anyway. What bothered him most in the play wasn’t when Romeo and Juliet died; it was when Mercutio died. In retrospect, the conversation was actually a little stressful, since he was afraid they were going to ask him if he was Catholic. His father was Catholic at one point, he tells us. He remembers a kid named Louis Shaney who was cool to talk to until Louis tried to subtly find out if he was Catholic.