Ok, here's one:
The PC's are standing in a field of waist high dead grass. A harsh, evil wind blows. In the distance, an army marches past.
Or would have.
One PC says, "I cast flaming sphere."
The DM, taking pity, says, "Well, it rained not *too* long ago (pushing the boundaries of realism, there), so the grass doesn't catch fire *yet*.
"Good," says the PC. "I cast another one."
Here's another:
Slydder, a stealthy type who's claim to fame is the ability to turn into a small, blind mole, is very angry at "D", a knight wannabe who owns one old horse, one suit of plate (painted black to hide the signs of wear), and one set of horse barding. These are both PC's.
They are hired as underlings by someone way more powerful than themselves, and at one point are instructed to "wait outside" while the NPC checks out a fortress. The PC's don't. Instead, the knight comes in *on his horse* *wearing full plate*. The ninja wannabe sneaks on ahead. When the big baddies show up, they see the knight (who's incredibly obvious), but not Slydder, though Slydder is closer. The knight, worried about what's about to happen and thinking Slydder won't come out of hiding to help, outs Slydder himself by pointing to his hiding place and saying, "Why don't you come out and fight like a man?"
Amazingly, they survive.
So later, Slydder tries to poison the knight. Unfortunately, he messes up. Now 2 PC's and a horse are poisoned. The two PC's, blinded, nearly dead, deep in the desert, crawl around taking wild swings in the air trying to hit one another. This goes on until they are too tired to move. They rest, but now the knight is having to make some serious CON checks; he's wearing black armor in the desert.
He refuses to take off the armor. In fact, he goes to remove the barding from his dead horse, and then tries to DRAG IT back to the nearest city. After a series of amazing CON checks, he finally dies due to heat, damage, poison, and exaustion within a few hundred feet of the city walls.
Meanwhile, Slydder gets to that city, and offers the poor barkeep FIVE PLATINUM to "keep guard" at his door while he goes to sleep. He does this in front of a bunch of poor, unruly looking townspeople. It did not end well.
AND FINALLY: (Almost) Total Party Kill in under 15 minutes
The PC's start out in and around a xenophobic city that tolerates nothing but humans. It is huge, well guarded, and has a fighting arena where dwarves, elves, and the like fight to the death for the citizens' amusement.
Two PC's (we'll call them "A" and "B") are dwarves. They are together and well armed, and they are simply passing by the city. They see the huge warning, in Dwarven, that Dwarves seen near the city walls will be executed. They see the guards. What do they do? They attack.
One is killed on the spot, the other is taken to fight in the arena. However, he acts up so much that the guards deem him too dangerous to work with, and so he ends up in an exposure cage. Two PC's down in under 5 minutes.
One PC (let's call him "C") starts out in the arena. He is strong enough to lift the heavy gate that his captors have just pushed him through, and has secretly made escape plans with several NPC's who are currently pretending to fight eachother in the arena.
PC "D" starts the game by being pushed into the arena just as PC "C" and the NPC's make a break for it. PC "D" lifts the gate, and the NPC's begin fleeing...but PC "C" says, "I was put in here to fight, right?"
DM nods.
PC "C" says, "I attack that guy holding the gate...his hands are full, so he can't fight back!"
The DM had been intending to be merciful; had those two escaped, they would have passed right by PC "B's" exposure cage and been able to rescue him. But alas, it was not to be.
There were 3 more PC's, played by a group of experienced players had been playing these characters for a while. Seeing how dumb the other PC's were being, they decided to abandon the campaign entirely, and simply teleported out.
Campaign over. 3 dead, 3 survivors, under 15 minutes.