I'd say "You dare use my own spells against me, Potter? It was I who invented them -- I, the Half-Blood Prince!" but that's the same scene as "DON'T CALL ME COWARD!"

So how about the scene from "Snape Victorious" after Dumbledore announced who would be teaching Potions and who would be teaching DADA:

"Snape, who was sitting on Dumbledore's right, did not stand up at the mention of his name; he merely raised a hand in lazy acknowledgement of the applause from the Slytherin table, yet Harry was sure he could detect a look of trimph on the features he loathed so much."