“What? You mean you don't want to pull an all-nighter?”
You're working on a project at work with a group of people. You're not finished with it, but everyone is tired and it's getting late, so someone suggests picking it back up the next day. You think that's a good idea, but you want to joke that everyone should stay all night to work on it, so you say this.
What? You mean you don't want to pull an all-nighter?
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What? You mean (clause)?
This is a common type of joke. A person will say, "What? You mean..." and then pretend to be surprised by something. For example, a woman might say to her boyfriend:
What? You mean you'd rather stay home and watch football than go shopping with me?
This type of joke makes the most sense when the thing that you pretend to be surprised about is something obvious. In the example at top, no one wants to stay at work all night. So it's clear that the speaker isn't really surprised that people want to go home.
You can also use "What? You mean ___?" seriously, when someone says something that surprises you:
What? You mean you're not coming with us?
pull an all-nighter
"Pulling an all-nighter" means staying up all night to work on something. This is most often used to talk about students who stay up all night to finish a big homework assignment or to study for a test. You can also use it when you're talking about people staying at work all night to finish something.