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. Differs from a Catch Phrase in that repetition is a key component of the Catch Phrase. The One-Liner is typically used once and never again.