My personal favorite is Imperial Balmorra, on the second level in a tent near the bank. I get disappointed when I can't trigger this one. Not emotional, except the Imperial's ridiculously gleeful last line. The voice actors really make it:
Imperial: Next! And you are?
Imperial: Let's see...ah, here you are. "Killer" Kateo. Butchered an entire Republic squad with...a shiv?
Prisoner: That's me.
Imperial: Someone get this man a blaster! Welcome to the Imperial Army, Kateo. And if you should need something say, dull or rusty, just let us know.
Actually, all of Imperial Balmorra has great flavor text.
That's Belsavis, actually, but yes. Good one.
I like on Nar Shaddaa (Imperial hangar area) (Paraphrased) :
Soldier 1: The Hutts are horrible! The things I hear they do to the Evocii.
Soldier 2: Have you ever MET an Evocii. They bloody deserve it if you ask me.
Soldier 1: That's cold.
Soldier 2: Go meet one. Then you can talk. Fifty credits says you end up shoving it in a gutter. Laughing.