There are all kinds of jokes that “everybody” already knows and has heard countless times, and assumes everybody else knows. And in certain circumstances, people regularly toss out punchlines that seem appropriate to the situation. Examples:
When you’re given a task nobody else wants, you may hear, “Today is YOUR day in the barrel.”
When you say, “We have a ton of work to do,” a lazy slacker is liable to snort, “What you mean WE, Kemo Sabe?”
When things are looking grim, a would-be optimist may quip, “Well, there must be a pony here someplace.”
What punchlines do you hear or use semi-regularly? You don’t have to share the joke(s), just the punchlines and (maybe) the context in which they’re used.
Not the actual punchline, but you know how sometimes someone will tell you something, and they’re talking fast/excitedly, so there’s no pause for you to ask them what they’re going on about? So you end up hearing some long, confusing story that makes absolutely no sense to you? My usual reply to something like that is, "[a couple seconds of silence] …Who’s on first?