Every school has secrets, and James knew all of them...
For a brief period of time, Dominique and Teddy dated. James found them in a broom cupboard, kissing each other madly. When Dom saw him she threatened to hex him. She didn't have too. James was to shocked by the sight of his shy cousin wrapping herself around Teddy. Nobody else knew, but Rose suspected when Dom cried after when Victoire and Teddy announced they were dating.
Rose sneaked out of her bedroom at night to hang out with Scorpios. They never did anything, but they just looked at the stars, and chatted quietly. They would kiss goodnight, and then slipped back to bed.
Roxanne smoked for a month behind the broom sheds. When James saw her she cried and stubbed out her cigarette, and has never lit one again.
Fred had a huge crush on Anna Bell, Katie's daughter. He used to ignore her constantly, and she would look crushed. When she was upset though, he got very aggressive and uncontrollable. When he ended up in detention for the fifth time, and asked for an explanation, he said that Anna's boyfriend had been messing her around. Professor Longbottom laughed, and let him go. As soon as he was out of the classroom he kissed Anna. James was the only one who wasn't surprised.
Hugo had a tattoo. He got drunk, and had a tattoo of a feather on his shoulder. James saw it while he was playing Quidditch, and Hugo swore that if he told anyone, he would hunt him down and hex him into next year, then shoot him just for laughs, and throw him in the lake. James was so scared he agreed to secrecy immediately.