After reading and posting to Princess of Canada's great thread: Most Amusing PC Deaths, I figured we could share those great moments in games that don't cause death, but get the table rolling anyway. Here's one of mine:
In RotRL, the PCs are in the depths of Jorgenfist, after just beaten the jotunblood hill giant into a near-death experience. Having the melded back into the earth, the PCs are left staring at the spot he sunk into, wondering what to do now. (Warning: GM licensing here). The trigger-happy Mystic Theurge figures that the meld into earth ability is similar enough to the spell meld into stone that if he does enough damage to the earth at the right spot, he can expel the giant. Reaching for his necklace of fireballs, he yells "everyone back!" A mad scramble ensues as everyone dashes for cover/hides behind the door/counts off safe distance etc.
The theurge then throws a 2d fireball getting exactly 3 points of damage...
Covered in dirt, crawling out from behind pillars, picking themselves up off the floor, the entire party turned their heads toward him with a collective "wtf, that's it!?!" The Mystic Theurge suffered much ribbing at the hands of the party for the rest of the night...
Teleporting into unknown area leads to bad roll.
Fortunately, the room the magic user was teleporting into had another room below it. Unfortunately, the roll was 6 feet low from target (also unfortunate, the player was 6'1", so DM ruled scalp and hair materialized inside the wood separating the floors. Then a fall of 20 feet.
Once I had a group that had a barbarian and cleric that had gotten drunk and wandered into some woods. A gnome wiz/rogue followed them and when the two drunkards got attacked by a giant spider the gnome used an illusion to make it look like a horse with the face of the gnome. The barbarian kept failing his will and the cleric had failed the poison check which rolled max STR-damage so he was out of commission. The barbarian fought the spider for some time the whole time it was masked as a gnome headed horse. The gnome finished the spider with a fireball before the barbarian got killed. He once again failed a will once the spider had died and turned back into a spider (the gnome dropped the illusion once the spider died so it now looked like a spider once more) when the barbarian returned to town he was constantly trying to convince people that there was a terrible monster in the woods with the head of a gnome and body of a horse that erupted in fire and changed into a spider once it was killed. He had dubbed this creature the Spinoza (the name of the gnome caster who had tricked the barbarian) Pony. He continued to retell this story in every bar and town that he visited. Many a laugh was had because of a gnome who fooled a barbarian. (these two were husband and wife so there were never any animosity between the two) I gave the party an extra 1000xp that day for making me laugh till my face hurt.