Donna: I feel like you might be on the spectrum
The Doctor: Of Human Emotions? Yes! I love those. Unless they suck then I'm not the biggest fan.
Donna: I meant, the Autism Spectrum, and now I'm positive. Congrats
something something ten was rarely wearing less than three layers representing his being very closed off and scared of vulnerability, while fourteen sheds his coat early on and has rolled up sleeves most of the time to parallel his being far more comfortable with his emotions and the vulnerability that comes with it or something idk
because obviously the doctor is about to blame donna for spilling the coffee, but he catches himself, backs off and apologizes. and it's not him catching himself in a "this is a pointless argument because i'm right and you aren't getting that so i give up" sorta way- because in that beat after, he isn't irritated, he doesn't start trying to figure out a way to reiterate his point. it's him catching himself in a "that was the wrong thing to say and i regret that" sorta way.
it's him catching himself becoming another one of the voices in donna's head calling her a screw up.
“I really do remember though. Every second with you. I’m so glad you’re back, cause it killed me, Donna. It killed me, it killed me, it killed me.”
The recognition of the fact that losing Donna was such a last straw for the tenth doctor though. He lost her, and Donna had been so perfect for him, and just…this line and the delivery is exactly about that.