Gambit - 1. A remark made to open or redirect a conversation. 2. Chess. An opening in which a player seeks to obtain some advantage by sacrificing a pawn or piece. 3. Any maneuver by which one seeks to gain an advantage.
Draco Malfoy never liked Harry Potter. Not even when he extended his hand to him before the Sorting. After all, they'd already clashed on the train. Draco had ended up looking pretty stupid. He hated people who made him look stupid.
But he knew his father would be proud if he wrote to say that he'd made friends with Harry Potter, the Boy-Who-Lived. He so wanted his father to be proud of him, so he swallowed his pique and extended his hand.
Harry brushed it off as though he were an irritating fly.
Their enmity was sealed there and then.