Why did it depress Holden when an old guy told him that his days at Pencey were the happiest days of his life?

You see, Holden didn't like Pencey to begin with. In fact,
he didn't like any of the prep schools he went to -  the teachers
were phony, and so were the students. He never applied himself, because he never cared.
When the older man was talking about the happiest days of his life being at Pencey,
Holden thought it was a load of crap, and was wholly annoyed with the guy. He really
didn't like him. Then, to top it off, the guy wanted to go see if his dang
initials were still in the bathroom stall when he'd carved them
there when HE used to go there. But, see, when he says "it depresses me", and "it kills
me", he's not only giving a hint on his case of teenage depression, he's also trying to
say, "it really pisses me off" "or it really gets me worked up", just in a different
sort of way. (At least, that's what I think.)