Minerva & Narcissa
"We could debate the subjectivity of the dark arts all day, and never reach a consensus," Narcissa said mildly. "Using your definition, nearly half of the spells and potions taught at Hogwarts would fall under the dark arts. Unless you propose to strike hexes, jinxes and curses from the Defense curriculum, and leave students wholly unprepared to protect themselves?" That wasn't even getting into Potions, Charms or McGonagall's own subject, Transfiguration. Gryffindors were so narrow-minded, it was maddening to debate with one.
Narcissa straightened her shoulders. "That may well be, but Professors are supposed to be objective and unbiased, or is that untrue? I can't help but wonder what sort of role model you are for your Slytherin students, when you're so obviously sure that many of them could turn out to be dark wizards." Her voice was less friendly than before, but perfectly controlled and measured. "I will be forever grateful that they have someone like Severus to stand up for them, to guide them. The alternative could be so much worse." It was very clear just what she thought of Minerva McGonagall, and she didn't particular care.
She turned and gave the exhibit one last look. "Now, you must excuse me. I must see that the staff have everything they need." It was an obvious excuse, but Narcissa couldn't stand this woman for one more moment. "Have a good evening, Professor."