Doctor: Fear. Loneliness. They're the big ones, Rose. Some of the most terrible acts ever committed have been inspired by them. We're not dealing with something that wants to conquer or destroy. There's a lot of things you need to get across this universe. Warp drive... Wormhole refractors...You know the thing you need most of all? You need a hand to hold.
Rose: [Seeing cat.] Oh! Aren't you a beautiful boy?
The Doctor: Thanks. I've been experimenting with back-combing...oh.
Rose: [Seeing him grimace.] What?
The Doctor: Nah, I'm not really a cat person. Once you've been threatened by one in a nun's wimple, it kind of takes the joy out of it.
The Doctor: Nobody else in this entire galaxy has ever bothered to make edible ball bearings, genius!
Chosen answer: The Master knows that deep down, he deserves death for the crimes that he's committed throughout his life, and since he regards The Doctor as his arch-foe, he expects it to be at his hands. The fact that The Doctor is still willing to forgive him for all of his crimes hurts him more deeply than death would.
Captain Defenestrator