Antimony: Do I have to?
Any line of dialogue which demonstrates remarkable wit and composure for someone in that particular situation. Whereas a normal person would freak out upon finding (for example) a pack of dogs mauling a dead lawyer, the main character gives a wry smirk and says, "Well, I always said the legal profession was going to the dogs," thereby proving that they're Just That Cool.
A good one-liner sums things up nicely by being hilarious or insightful. Insight can be provided by what can it imply, often ones with philosophical meanings or its ease to be manipulated to one’s usage, usually by being (too) simple.
Differs from a catchphrase in that repetition is a key component of the catchphrase. One of these, that is not also a catchphrase, is typically used once and never again. Unless it memetically mutated, of course.
- Bond One-Liner: Just after killing someone.
- "Facing the Bullets" One-Liner: Facing down death.
- Faux Final Line: Delivered to give an illusion of normalcy.
- Incoming Ham: When a character enters the scene.
- One-Liner Echo: When it is reinforced by immediate repetition by others (non-immediate repetition by the same character elevates it to a catchphrase).
- One-Liner, Name... One-Liner: When it is addressed to a character and then repeated by the original speaker.
- Parting-from-Consciousness Words: Immediately before passing out.
- Pre-Asskicking One-Liner: Just before a fight.
- Pre-Mortem One-Liner: Delivered just before the killing blow; in other words, used to end fights.
- Quip to Black: Used to segue into a commercial break.
- Schiff One-Liner: Used to end an episode in a rather dark way.
- Wham Line: When a single line of dialogue dramatically alters a specific scene or even the entire work.