Garak

Doctor Bashir: They broke seven of your transverse ribs and fractured your clavicle.

Garak: Ah, but I got off several cutting remarks which no doubt, did serious damage to their egos.

Dr. Bashir: What I want to know is, out of all the stories you told me, which ones were true and which ones weren't?

Garak: My dear Doctor, they're all true.

Dr. Bashir: Even the lies?

Garak: Especially the lies.

Garak: When the Klingons attacked the station, Gul Dukat and I were fighting side by side. At one point, he turned his back to me, and I must admit that for a moment, he made a very tempting target.

Odo: You'd shoot a man in the back?

Garak: Well, it's the safest way, isn't it?

Bashir: It's a children's story, about a young shepherd boy who gets lonely while tending his flock. So he cries out to the villagers that a wolf is attacking the sheep. The people come running, but of course there's no wolf. He claims that it's run away and the villagers praise him for his vigilance.

Garak: Clever lad. Charming story.

Bashir: I'm not finished. The next day, the boy does it again, and the next too. And on the fourth day a wolf really comes. The boy cries out at the top of his lungs, but the villagers ignore him, and the boy, and his flock, are gobbled up.

Garak: Well, that's a little graphic for children, wouldn't you say?

Bashir: But the point is, if you lie all the time, nobody's going to believe you, even when you're telling the truth.

Garak: Are you sure that's the point, Doctor?

Bashir: Of course. What else could it be?

Garak: That you should never tell the same lie twice.

This incident from Broken Link, where Garak tries to destroy the Founders' homeworld.

GARAK: You're a Klingon: don't tell me you'd object to a little genocide in the name of self-defense.

WORF: I am a warrior, not a murderer.

GARAK: What you are is a great disappointment.