Regulus was certain that he was being punished. There was no other reason that would explain, out of the entire island, why James would have to be in the same location he was. Maybe there was something else to the Horcrux potion. Maybe it had trapped him somewhere where he was forced to live with his stupid sodding brother who could only shout at him and his stupid sodding brother's best friends, who either liked to string him along or defend Sirius after every twist and turn and every hour of the night. Regulus was nearing his breaking point. His hands tightened reflexively over the handle of the broom that he was holding. But, at least, he thought, there was no way that James would have the nerve to talk to him. Even James Potter had to have some common decency. The only one he could possibly decide to try and initiate a conversation was to either apologize or make some kind of excuse for what had happened.
And, of course, James, opened his bloody mouth anyway and didn't say anything of the sort. Regulus could feel his insides twist up a bit. He didn't understand how James could do it - how he could just pretend that everything was all right, as if nothing out of the ordinary had happened. Maybe he just lived his whole life by lying to himself. It was the only way that Regulus could think of that would allow for such behavior. He wanted to tell James to sod off or that he had some nerve saying anything at all, but Regulus said nothing at all. He didn't look toward James. He didn't acknowledge James. He knew this strategy wouldn't work very long, because James hated to be ignored, but Regulus wasn't going to play along in another one of his games. He was going to make idle chit-chat with James just to make him feel better about the fact that he had been an utter arse.
Regulus stopped from where he was sweeping entirely, turned back around and headed up the street in the opposite direction. He'd had enough of James' games and pranks to last him a life time. He was done this time.