My favourite scene is when Hazel and Isaac give their "pre-funeral" eulogies for Augustus.

“What a slut time is. She screws everybody.”

“You gave me a forever within the numbered days, and I'm grateful.”

“Grief does not change you, Hazel. It reveals you.”

*spoiler alert* (skip this bit if you haven't read the book, although I'm sure the whole world by now knows what happens at the end and it's predictable anyway )

“'I'm telling you,' Isaac continued, 'Augustus Waters talked so much that he'd interrupt you at his own funeral. And he was pretentious: Sweet Jesus Christ, that kid never took a piss without pondering the abundant metaphorical resonances of human waste production. And he was vain: I do not believe I have ever met a more physically attractive person who was more acutely aware of his own physical attractiveness.
'But I will say this: When the scientists of the future show up at my house with robot eyes and they tell me to try them on, I will tell the scientists to screw off, because I do not want to see a world without him.'"