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Let's just cut right to the chase. Does Mr. Antolini come on to Holden? The answer is … it's not clear.
There are definitely some hints that something is up here. We know that Mr. Antolini's wife is much older than he is, that she’s unattractive, and that she has a lot of money: in Holden’s terms, “She was lousy with dough. She was about sixty years older than Mr. Antolini, but they seemed to get along quite well” (24.1). While the two kiss a lot in public, they're never in the same room together, which makes us wonder if they're making a public show of what privately may be a marriage of convenience.
Mr. Antolini calls Holden "handsome" before heading off to bed—“forgetting,” by the way, to give Holden pajamas, which means that he has to sleep in his underwear, and also making a comment about his “long legs” after quizzing him about girls—and then sits next to him in the dark (while Holden's sleeping), and pets his head. When asked about it, he pretends things are casual, but lets slip a "I'm simply sitting here, admiring" (24.79). And then, he tries to shift the focus to Holden, accusing him of being a "very, very strange boy" (24.89).
On the other hand, Holden and Mr. Antolini have been friends a long time, and the two are obviously close. They used to play tennis together, Mr. Antolini hangs with Holden's parents, and we can tell from his lengthy discoursing that he cares a lot about his former student. Maybe "handsome" was just a compliment. Maybe Mr. Antolini was just been drunk and sleepless. Maybe he’s just worried about the kid’s future. And maybe he’s attracted to Holden’s youth—just the same way Holden is attracted to those kids at the park. Maybe he looks at Holden, he sees someone who hasn’t made the same mistakes or questionable life choices Mr. Antolini has, like marrying an ugly old lady for her money.
As it turns out, we have to choose not only how to interpret this scene, but also how to interpret Holden's subsequent comment that "When something perverty like that happens, I start sweating like a bastard. That kind of stuff's happened to me about twenty times since I was a kid" (24.94). Twenty times? Holden is prone to exaggeration, but is there a chance this could be true—especially if Holden is giving off some vibes of his own?
But what, exactly, falls into Holden's category of "perverty" behavior? If Holden actually has been come on to more than once, and maybe even molested (all those prep schools …), we can understand why he always sees sex as degrading. But if Holden just thinks that normal behavior is "perverty," the problem is with him, not his environment or circumstance.
And then there’s Mr. Antolini’s lecture on education, which basically boils down to his last comment: “If you go along with it […] it’ll begin to give you an idea what size mind you have […] After a while, you’ll have an idea what kind of thoughts your particular size mind should be wearing. For one thing, it may save you an extraordinary amount of time trying on ideas that don’t suit you, aren’t becoming to you” (24.59).
Even if Mr. Antolini’s intentions are questionable, he’s making a reasonable argument. We'd go ahead and argue that it sounds like the tone here is genuine: it doesn't seem like the author is poking fun at this set of beliefs in any way, like he does with Holden’s other teacher Mr. Spencer. This just might be the real deal. And interestingly, Holden doesn't make sarcastic comments in response. He's tired, and he doesn't exactly applaud the speech, but he doesn't berate it as being phony either.
What does it mean, then, if the one person (besides Phoebe) who offers Holden real emotional help ends up trying to take advantage of him sexually? Or, what does it mean for Holden to imagine that this one person is trying to molest him? Either way, it look pretty grim for our boy.