"And you think you do?" Harry shot back. He straightened as Draco pushed past, shoving back just because Malfoy had started it. "That's what you think," he added. Even though it wasn't true, and he'd likely feel a bit guilty about that later. But if anyone deserved to be paranoid about being watched, it was Malfoy.
He deserved loads worse than that, actually.
"Could fill a whole bloody room with shite you have no clue about, Malfoy. Bet they don't even tell your dad much, since he's just an evil errand boy. Junior errand boys don't even get told that much. Just what to do." It was probably less effective, since it was barked at Draco's back.