A common trend for characters in works of fiction is to shrug off danger or laugh at it. In totally serious drama, characters might be crying in fear or "shell-shocked" from life-threatening situations, but in any other genre, characters react to danger in any number of more calm ways:
Crack a joke or make a sarcastic comment about the danger.
Crack a joke to get people's attention. (e.g. someone hanging from a cliff says "Hey guys? Over here!")
Argue or speak casually while the danger is going on, usually about something tangential. Bonus points if the argument briefly stops for one of the heroes to shout "look out!" and then resumes shortly afterward. Points also awarded if a character in danger suddenly focuses on a complete non-sequitur to the action ("Your hair looks fantastic!").
Act as if the danger is real in their dialog, but speak calmly about it. See also This Is Gonna Suck and Danger Deadpan.
Depending on how it's handled, the first three occur most often in comedic shows, while the last one is most common in shows that don't lean too far towards humor, or want to be more realistic. The first three also happen fairly often in more serious works, but often with an edge of sarcasm or bitterness, implying that the hero isn't feeling particularly mirthful about the situation.
There's some truth to this. People in real life professions such as police or military become so used to life-threatening situations occurring every week, or even multiple times a day, that they end up engaging in Casual Danger Dialog all the time. For example, Evan Wright's nonfiction book Generation Kill has accounts of United States Marines under heavy machine gun and mortar fire and in the middle of pitched gun battles remaining calm under pressure. Even ordinary people can end up this way, as it's well-known that many people use humor or sarcasm as a way of coping with stress or fear; see Gallows Humor, Stiff Upper Lip, and Street Smart.
Usually done for comedic effect in comedies, naturally. May involve some amount of Acoustic License. Compare Talking Is a Free Action. See also Distracting Disambiguation. Contrast Say My Name and Big "NO!", which involves meaningless exclamations that can seem as unrealistic as a quip. Truly Failure Is the Only Option when dealing with dramatic dialogue. The other intended effect is to communicate just how used to these situations the heroes are. When things are so bad that they don't do it, see Sarcasm Failure. If the person receives a phone call during a tense situation, and picks it up to complain about the timing of the call, see Kinda Busy Here. See Seinfeldian Conversation and "Cavemen vs. Astronauts" Debate for meandering/meaningless arguments to be had in situations such as this.
A Sub-Trope of Bathos. Sister Trope to Flirting Under Fire and Snark-to-Snark Combat. Compare Opponent Instruction. Super-Trope of Combat Uninterruptus (having a conversation during a fight).
