What seems to give Johnny the most pain in his life in The Outsiders?
Johnny has two major problems that make him miserable: He feels unwanted and unloved by parents, who argue relentlessly at home and even beat him when they are angry. He also worries about being jumped by the Socs, who have already given him a severe beating before. Johnny seems happy only when he is hanging out with his greaser pals, feeling secure that he will be safe from harm when they are together. He is the "gang's pet, everyone's kid brother," since they are well aware of his rotten home life.
His father was always beating him up, and his mother ignored him, except when she was hacked off at something, and then you could hear her yelling at him clear down at our house. I think he hated that more than being whipped. (Chapter 1)
As for the beating he takes from the Socs, it makes him "jumpier than ever. I didn't think he'd ever get over it. Johnny never walked by himself after that." And he takes to carrying a knife, ready to "kill the next person who jumped him." After he kills Bob Sheldon, Johnny finds that he has several more problems: He is being hunted by the law and he feels tremendous guilt about knifing Bob.
"I killed a kid last night... How'd you like to live with that?" (Chapter 5)