I can't think of an NPC who does more smack-talking than the awesome HK-47!

HK-47: "Retraction: Did I say that out loud? I apologize, master. While you are a meatbag, I suppose I should not call you such."
Revan: "You just called me a meatbag again!"
HK-47: "Explanation: It's just that... you have all these squishy parts, master. And all that water! How the constant sloshing doesn't drive you mad, I have no idea."

Revan: "Are you deliberately trying to insult me?"
HK-47: "Answer: Deliberation implies some form of intent, master, when I am only stating a fact. Perhaps you would prefer the term liquidious fleshbag?"
Revan: "How about 'human'?"
HK-47: "Objection: But... but that technical term does not accurately portray the vast amount of bulbous slushiness present in your bipedal form!"

HK-47: "Commentary: How would you like to be the wholly-owned servant to an organic meatbag? It's demeaning! If, uh, you weren't one yourself, I mean..."
Revan: "Demeaning, is it?"
HK-47: "Qualification: Err... perhaps I did not mean it quite like that, master. I mean... while an artificial life-form is superior..."
Revan: "You're not making it any better."
HK-47: "Commentary: I mean... nice human, goo-oood human..."

HK-47: "Shall we find something to kill to cheer ourselves up?"

HK-47: "Query: Can I kill him now, master? I would like ever so much to crush his neck, just a little. It is a long-time fantasy of mine."
Revan: "Maybe later."
HK-47: "You hear that, meatbag? I will be back!"

HK-47: "Suggestion: Perhaps we could dismember the organic? It would make it easier for transport to the surface."
Mercenary: "Hey! Y-you... you can't just rip me to pieces! I'll die!!"
HK-47: "Amendment: I did forget that. Stupid, frail, non-compartmentalized organic meatbags!"

HK-47: "Observation: We can begin by slaughtering the inhabitants of this building, master. Would that be impressive?"
T3-M4: "Beep-Beep Boop Boooop."
HK-47: "No, I didn't mean us as well, you moronic droid."

Revan: "You are just a traveling piece of bad luck, aren't you?"
HK-47: "Objection: That is so unfair, master! Have I not brought you a great deal of satisfaction?"
Revan: "You don't want to hear the answer to that."
HK-47: "Statement: You are a very harsh master, master. I like you."

HK-47: "Commentary: Your former pupil is efficient and brutal, even for an organic. I rather liked him when you first introduced me to him. If I had known what he would do to you, master, I would have gladly removed his entrails right then!"