The word “elite” is used in a derogatory manner in chapter 3 when the boys are at the drive-in theater.
There are two main social classes: the Socs and the greasers. The “Socs” are the elite, higher than middle class. They have money and power, and they use it to target the greasers. The greasers clearly resent them for it.
"And," Two-Bit added grimly, "a few other of the socially elite checkered-shirt set." (ch 3, p. 41)
The word “elite” implies special privileges. In this context it is an important distinction because Johnny, Ponyboy and Two-bit are hanging out with Soc girls on a more or less equal level until they see their boyfriends coming. The girls try to avoid their boyfriends, reminding Two-Bit and the other greasers that they are less than the elite.
The use of this word at this point in the story is crucial. A main theme of the book is that people are the same on the inside. As Ponyboy notes, they see the same sunset. Yet the presence of the boyfriends reminds the boys that although they have been hanging out with the Soc girls, they are still not equals. They are less than elite.