Not really funny in the traditional "ha ha" sense, but many years ago My friends and I had a DM who was very bad at his job. As in he couldn't deal with it well when players didn't follow the story the way he thought we should.
He was also really bad at keeping things in check, allowing us to make rolls on things that he probably should have just said were impossible.
So we are walking through the dungeon of grimdark on our way to kill the slavering beast of madeupia.
Along the way we find a blue potion in a bottle. The label says potion of freezing. In the DM's own words, this potion is 100% guaranteed to freeze anything.
Later on, we come to a room full of lava. Apparently, we were supposed to use the potion of freeze anything to freeze the lava. We didn't do that. Instead, we manage to jury rig a rope bridge across this pit of lava, using stone pillars and stalactites to secure our ropes. (See what I mean about rolls we shouldn't have been allowed to make?)
The DM gets very upset and we don't meet for 2 weeks after that. We forget all about the potion.
When we do reconvene, we continue to hunt for the slavering beast of madeupia. Eventually we find the beast and kill it, and then proceed into the final room which presumably held the exit. The reason I say presumably is because we never got out of that room.
The room was described as having a roof approximately 8 times the height of the Sistine chapel, being supported by several rock pillars. As we walk into the centre of the room, one of the pillars comes to life. It's a rock golem, roughly 20 stories tall. We attack the rock golem.
After several rounds of combat, our warrior has broken his sword due to a critical failure, our paladin is dead due to being stepped on repeatedly, our wizard has exhausted his spell repertoire to no effect and our ranger has been knocked unconcious by falling rocks.
Our rogue searches desperately for something to help us defeat this monster, when he double checks his inventory and finds the potion of freeze anything. He throws the potion at the golem.
The conversation goes as follows.
DM - The potion hits the golem on the right leg. The golem freezes in an instant, completely imobilised.
Rogue - Oh yeah, who saves the day? It's me. I'm so claiming a tithe of your rewards for saving all of y..
DM - It falls on you. You all die.
Rogue - What? Bullshit! I make a dodge roll.
DM - It's 20 stories high. It's to big to dodge. You're dead.
Rogue - But..
DM - Dead. All of you. Forever.
Turns out there was an elaborate Rube Goldberg machine waiting in the wings for us to use to defeat the golem. Apparently the first step to kicking off this machine was to pull a lever hidden in shadows on the far wall of the cave. Where none of us could see it. On account of us being distracted by the freaking huge rock golem in the way.
Suffice to say, we don't play with that DM anymore