This is purely hypothetical, just for fun. In this scenario, you don’t get to know who the GM is in advance, but they do have to run it as written. The players can leave whenever they like, but the GM has to stay until either all players leave or the players beat the dungeon.
I start by making a map. I am terrible at making maps. I try to improve my map by using a transparent quilting ruler, defining a scale, and carefully noting the measurements of all the rooms. I somehow manage to change my scale several times during this process, write down the wrong measurements, and get confused about which lines are which on my quilting ruler. Complicating matters, my quilting ruler is big and heavy, and slips around on the page. (Naturally, I don’t notice).
Since my dungeon has multiple levels, I am very careful to include staircases, which, since none of the floors are the same size and shape, don’t actually join up from level to level. I notice that everything looks a little sloppy, so I go over it in pen, and erase the pencil lines. This makes it look nicer. It also destroys any last traces of geometric plausibility.
When I’m finished, my Escher-esque monstrosity is so impossible to navigate that it doesn’t even need monsters. The entire party will just get sucked into the treacherous anti-grid of the map itself, and never be seen again. If the GM asks me to explain the map so they can extract the players, I will be unable to do so, since I have a terrible memory, and can’t read my own handwriting.
This is magnificently evil. It’s also extremely specific, to the point I’m worried this happened in your life.