I have a pretty good one. I DM for a party of four in a homebrew campaign, consisting of a ranger, sorcerer, Cleric, and a knight. The party has at least one problem with each character. The sorcerer never plays seriously, the ranger can barely hit ANYTHING, the cleric always focuses a little too much on dealing damage, and the knight has a superiority/ god complex and anger issues.
The party had just been in an encounter with the first main boss and was magically teleported to an underground lake filled with puzzles. The party has basically no problems with any of them, but in the very last area there was a drider. The party did fine for a while until the knight started to go for her signature combat strategy in which she would climb a wall while an enemy was distracted to get above them and drop down, impaling the enemy with her glaive. She succeeded in impaling the drider and began riding on its back.
At this point, her turn ended and it switched to the sorcerer's turn. He had already run out of spells so he decided to throw a javelin, despite the knights warning about the possibility of hitting her instead of the drider. He rolled and got a nat 1, to which I briefly laughed at before slowly turning my head to the knight and telling her to roll a reflex save. She rolls and gets a 5 overall (rolled a 2).
The javelin hits her in the shoulder and I proceed to ask for a Balance check. To everyone's horror, the dice landed on 1 and i told her that she fell off, without her glaive, and broke her leg to the degree where her leg was limply dangling and the bone could be seen. So she was now left without a weapon and could not stand. The sorcerer still had a move action and decided to run to the knight to hand her his remaining javelins.
But as he ran he attempted to tumble past to avoid the attack of opportunity. He rolled another 1, causing him to fall on his face directly in front of the Drider. It was allowed an attack of opportunity and got a critical, which K.O.'d the sorcerer. I was laughing in awe at this point, and it was now the cleric's turn. He ran towards the Drider readying his dwarven urgrosh and rolled an attack.
It happened again, another 1, he rose his axe in the air and the blade flew off, traveling straight up. As it came down, I asked the cleric for a reflex. Can you guess what number it landed on? Another... 1. The axe blade came down hard, smashing into the top of his head, knocking him unconscious, and causing him to topple to the ground. The ranger was now the only one left to attack and he decided to throw his dagger which he rolled a one for.
At this point i was actually worried that the party might die to themselves. I asked him to reroll that attack and, shockingly, the d20 landed on another 1. The dagger bounced off of the glaive that was still stuck in the drider's back and hit the ranger in his left eye, completely blinding him (he was already blind in one eye as part of his backstory). This was looking very bad as now, the entire party was disabled, and the only player that could do anything had a horribly broken leg. I really didn't want the party to die like this, they were barely even into the campaign and they were about to die because of the longest string of critical failures ever.
It was now the drider's turn and it moved to the ranger, got a critical, and knocked him out. It was once again the knight's turn. Not knowing what to do, she looks around until she spots the sorcerer's javelins on the ground. She slowly crawls over and picks up a javelin and rolls her attack. She... got... a... 1. At this point i was running out of ideas for nat 1's, so i told her to roll an intelligence check. She has low intelligence, giving her a -3 modifier, so she rolls a 2, which came out as a -1. She suddenly forgot how to breathe, dropped the javelin, and was now flailing around wildly in panic.
I knew that the would die if i didn't just BS something right then, so as they were all unconscious/ dying in the dumbest way possible, i said a beam of light shone down in front of the drider. And from the heavens descended a chicken in tin foil armor; the chicken proceeded to peck the drider once, causing it to explode for no apparent reason. The chicken then slowly ascended before disappearing into the light. The party was hysterically laughing and horribly confused.
To this day, the party is alive and nearing the end of my campaign, but after that, the party began a tradition of offering 500 gold a person to what they call "Stan the Battle-Chicken" monthly. Also, after that God awful session, we put all of their d20's through our washing machine to rid them of whatever curse they had picked up.