Kat: Now say something witty to the Enigmarons and finish the mission!
Antimony: Do I have to?

"Enough is enough! I have had it with these motherfuckin' snakes on this motherfuckin' plane!"

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 ones usage, usually by being (too)simple.

Differs from a Catch Phrase in that repetition is a key component of the Catch Phrase. A One-Liner that is not also a Catch Phrase are typically used once and never again. Unless it memetically mutated, of course.