To what does Holden compare Phoebe’s behavior when she finds out that he was expelled from Pencey Prep?

Phoebe's none too impressed with Holden for getting himself kicked out of Pencey Prep. She's probably lost count of the number of schools from which her brother's been expelled, and each time Holden gets his marching orders, she sees this as further proof, if proof were needed, that he just will not grow up.
Holden tries to blag his way out of the situation, blithely telling Phoebe that he'll most probably be sent to military school—if he's still around, of course. But Phoebe turns the conversation back to the matter at hand, which is Holden's immaturity. In response to Holden's claim that he didn't like Pencey Prep, Phoebe challenges him to name one thing that he does like. The fact that Holden can't give a convincing answer—even if he does supply us with the meaning of the book's title—speaks volumes.
Holden's not prepared to take any responsibility whatsoever for his actions. Instead of facing up to the part he's played in getting himself expelled, he compares Phoebe's behavior to that of the members of the Pencey Prep fencing team who ostracized him after he left behind their equipment on the Subway.