Mr. Antolini comes at the very end of a long list of characters who Holden judges to be "phony," which is a kind of all-inclusive term he uses to denote a level of hypocrisy, shallowness or pretense that he finds to be unbearable. What is made particularly worse in this case is that Mr. Antolini is an adult figure whom Holden respects and confides in. What Mr. Antolini does to prove himself to be phony is to try and make a homosexual advance towards Holden whilst he is sleeping on his couch at night:
I woke up all of a sudden. I don't know what time it was or anything, but I woke up. I felt something on my head, some guy's hand. Boy, it really scared hell out of me. What it was, it was Mr. Antolini's hand.
Holden responds instinctively, getting dressed straight away and leaving the flat. To him, this is the final proof of all adults being phony, as Mr. Antolini was almost a kind of quasi-father figure to him. He however has shown himself to be just as phony as all the other characters, as he pretends to be heterosexual and performs this role to society, whilst secretly being homosexual.