"I would've given you so much sugar," James said, grinning up at him. "'Cause you're my sugar, Sirius."
Which was actually rather accurate in a simply literal way; Sirius kept him young and energized and on his toes. But he also meant it in that he loved his best mate to pieces. He absolutely, positively intended for it to be taken both ways.
He made a face, though, and tried to playfully smack Sirius, which of course didn't work because his hands were still pinned. "That's the weirdest bit, he isn't," he said. "He's so shy and nervous all the time. If you called him names at this age, he might actually cry."