What do the following quotes from The Catcher in the Rye mean? "That's the whole trouble. You can't ever find a place that's nice and peaceful, because there isn't any. You may think there is, but once you get there, when you're not looking, somebody'll sneak up and write 'F*** you' right under your nose," and "Don't ever tell anybody anything. If you do, you start missing everybody."
The first quote has to do with Holden's desire to preserve the purity of childhood. A grade school is a place that should be free of adult profanity. It really offends him, he feels physically shaken when he sees these vulgar words written on the walls.
The museum also has a link to Holden's childhood and his sister, he loves the place because everything there stays the same. It is frozen in time, eternally set in place, reflecting a place and time in the past.
The second quote is the last line of the novel. Holden regrets having told the story to the reader, because now, as a patient in the mental institution, he misses his old life, even Stradlater and Ackley. He misses everyone he talked about, so he warns the reader to not talk about memories, they only remind you of what you no longer have.
The first quote speaks to Holden's concern with his own adolescent loss of innocence and his desire to protect children like his sister in their own innocence. When he arrives at his old school to deliver a note to Phoebe, he sees "f**k you" written on a wall. He rubs it out, then sees a second iteration elsewhere in the school. This one is etched in, perhaps carved with a knife, and he can't erase it. He can't, in other words, remake the world to be innocent. At a nearby museum, undoubtedly the Metropolitan Museum of Art, he meets two boys who have skipped school and want to see the mummy exhibit. They chicken out, and alone by himself in the exhibit, Holden begins to feel peaceful. Then he sees the words "f**k you" again. This is where the first quote enters: Holden can find no place of innocence in which he can escape adult knowledge. He can't return to the childhood garden of Eden. He is living in a fallen, imperfect world, and the words "f**k you" come to represent that fallenness to him.
In the second quote, the last line of the novel, Holden is feeling the pain of memory. His "missing everybody" suggests that he is feeling positive emotions towards other people, even people he dislikes. This ability to feel and have some nostalgia for his old life signals hope for his recovery.