The trouble with computers, of course, is that they're very sophisticated idiots. They do exactly what you tell them at amazing speed. Even if you order them to kill you. So if you do happen to change your mind, it's very difficult to stop them from obeying the original order. [stops computer from destroying Earth] But not impossible.
S12 E1Robot
S12 E2The Ark in Space
You're a clumsy, ham fisted idiot!
I said I was sorry!
What?! Come out. And don't touch anything!
I was only trying to open the door!
You haven't touched anything, have you Harry?
Me?!
Well, there are only two of us here, and your name is Harry!
Aren't you feeling better?
[Holding his head] No I'm not!
Well pull yourself together, man, this is fascinating!
You claim to be Med-Techs?
Well, my Doctorate is purely honorary and Harry is only qualified to work on sailors.
Steady-- Steady on, Old Girl! Steady on...
Harry...
Yes, I'm here, I'm here.
Call me 'Old Girl' again... And I'll spit in your eye.
Welcome back, Sarah Jane!
Homo sapiens. What an inventive, invincible species. It's only a few million years since they crawled up out of the mud and learned to walk. Puny, defenceless bipeds. They've survived flood, famine and plague. They've survived cosmic wars and holocausts. And now, here they are, out among the stars, waiting to begin a new life. Ready to outsit eternity. They're indomitable. Indomitable.
I might've been saying something important. (horrified expression) I was saying something important!
The Ark was designed to have a negative fault capacity.
Gremlins can get into everything, old girl. First law of the sea.
[The Doctor corrects the fault]
There you are, what'd I tell you? The Doctor's a first class boffin!
(Muttering to himself)
What?
He sometimes talks to himself, mostly because he's the only person who knows what he's talking about.
RRogin
There’s been a snitch up. Didn’t I tell you, Lycett, I said five-thousand years ago, I said there’d be a snitch up.
LLycett
[cuts in] Ten thousand.
RRogin
Ohhh, beautiful! I said we should have taken our chance with the solar flares and gone into the thermic shelters. We’d have been happily dead by now.
Doctor, the fate of all humanity might be decided within the next few hours.
Vira, if you fail, your people will die in pain and fear. If I fail, they'll die anyway. But at least only the six of us will know anything about it.
RRogin
We should have stayed on the earth, Lycett. I liked the earth. I like heat!
It may be irrational of me, but human beings are quite my favourite species.
[Harry is feeding cord to Sarah, who is climbing through tight tunnel; she stops]
How are you doing, old girl?
[hisses back] How do you think I’m doing, twit?
[affronted] Sorry, I thought you were stuck.
These quotes come from Wikiquote's Doctor Who pages and are available under the Creative Commons Attribution-ShareAlike License.