Ponyboy was bothered by his school friends seeing his house because most of them came from "good homes, not filthy-rich like the Socs, but middle-class anyway" (163). Ponyboy's concern come from the fact that he knows his house and neighborhood are not very nice; in his opinion, the house is "run-down looking [...] and the inside's kind of poor-looking too" (163). He is insightful enough to realize that most of his middle class friends come from much nicer looking and more well-cared for homes, so Ponyboy is a little ashamed for them to see his house in comparison. He likes his friends from school, so their good opinion matters to him.
On the other hand, Ponyboy "couldn't have cared less about what Randy thought," because Randy is an outsider to him (163). His opinion does not even register to Ponyboy, because he does not even have a real relationship with the Soc boy. The difference between Randy's opinion versus Ponyboy's school friends' opinion about his home comes from Ponyboy's own perception of whether or not the person matters to him personally. Randy's opinion does not matter to Ponyboy, because Randy as a person is equally unimportant to him.