In The Catcher in the Rye, where is this quote coming from and what is the situation? Also if you happen to the know the page number, please provide it? “When you're not looking, somebody'll sneak up and write 'F*** you' right under your nose.”
The quote you refer to in J. D. Salinger's The Catcher in the Rye is to be found in chapter 25, close to the end of that novel. In my paperback edition of the book the exact words are to be found on page 204. Holden has left a note for his sister Phoebe at her school asking her to meet him at the Museum of Art at a quarter past 12. He actually sees the words "F*** you" for the first time on the staircase at her school in chapter 25, and then sees the same words on a different staircase when he is going down after delivering the note.
The first time he sees the words he is infuriated because somebody wrote them in a school where little children would read them, but by the time he sees them at the museum they only seem to make him feel hopeless and depressed. Yet Holden's New York of the early 1950s seems like a better place than New York or any other big city today--for who would think of asking a ten-year-old girl to leave her school in the middle of the afternoon and travel some distance all by herself to meet him in any big American city today?