Here's one of my favourite bits of dialogue from Serenty (the ep):
Simon: I'm trying to put this as delicately as I can... How do I know you won't kill me in my sleep?
Mal: You don't know me, son, so let me explain this to you once: If I ever kill you, you'll be awake. You'll be facing me, and you'll be armed.
Simon: Are you always this sentimental?
Mal: I had a good day.
Simon: You had the Alliance on you, criminals and savages... Half the people on the ship have been shot or wounded including yourself, and you're harboring known fugitives.
Mal: Well, we're still flying.
Simon: That's not much.
Mal: It's enough.