Ponyboy is explaining how people don’t suspect the Socs because they are rich kids who dress nicely and don’t look like they are headed for trouble.
As they arrive at the rumble, Pony realizes that the Socs do not look like rumble material.
They looked like they were all cut from the same piece of cloth: clean-shaven with semi-Beatle haircuts, wearing striped or checkered shirts with light-red or tan-colored jackets or madras ski jackets. They could just as easily have been going to the movies as to a rumble. (ch 9, p. 142)
This demonstrates one of the major themes of the work: people judge you by your social class. Pony and his friends look like hoodlums, and are treated as such. The Socs look like nice boys, and no one suspects them of anything. They are only troublemakers while they are young, and then they go on to college and responsible adulthoods.
They have futures, while the greasers do not. Pony is tired of this. He is tired of the constant fighting. All he can think about is Johnny, lying in the hospital, because some obnoxious Socs jumped them and forced them to go on the run.