"Why Miss Cho Chang don't you know my greatest trait is the ability to survive?" By many accounts from his peers, Zacharias Smith was a horrible Hufflepuff, but there was a reason why his patronus was a badger. He could hold his own and be just as vicious if he needed to - when it came to something he wanted he was going to fight for it no matter what. And even in it's current less than spectacular state, he valued his life and would fight to defend himself.
"I always thought that was something you liked about me, considering your history." Maybe this would have gone better if she wasn't coming at him with kids' gloves, keeping him at a distance withe professional even tones. Although it would have been somewhat hypocritical to call her on it because he did the same thing only instead of clipped tones he used snide remarks.