I started playing through a second time yesterday, this time as a renegade. With this thread in mind, I'm playing with a notepad near me to keep me occupied during the loading screens.
Here's a few so far:
Shepard to a Krogan receiving smuggled shipment on Noveria: "If you want to see more of the package than me beating you with it, make me a better offer."
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The same Krogan after you decline his best offer: "You probably couldn't even figure out how much more you'd be getting from me. Stupid base 10 math, that's what you get for having more fingers."
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Shepard to a harmless corporate doctor on Noveria: "Someone in here needs a punch in the throat."
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Biased reporter on the Citadel: "I'd like an interview, whattaya say?"
The conversation option text says "I say get stuffed", although he says something different when you choose it.