I have a few, both as player and as GM.
Player:
1. We are high level(ish) heroes facing off against an invisible cultist. My bard is the only one who can see the cultist. "I can reveal him with Glitterdust," I say, "But I'll get everyone else in the team!"
"Do it!" the wizard orders.
"Okay...," I answer. I cast Glitterdust at the rest of the team, save DC was around 22, blinded the wizard, fighter, and cleric; cultist saves. Don't worry, the barbarian-tank killed the cultist.
2. A rakshasa detonated a fully loaded Necklace of Fireballs type VII in my barbarian's face. Character got mad. Rakshasa cast two fear-type spells. Barbarian got very mad. Rakshasa decides to teleport before barbarian kills him.
3. Learning that PF Enlarge Person lasts a minute per level and it takes only a standard action if you drink it as an extract.
The pirates are bringing a prisoner into a seaside cave. The lock up the prisoner in a pillory. We rappel into the cave commando style and begin slaughtering pirates. Using this new found knowledge, I turn into giant Tengu Alchemist of Terror and start chopping pirates in half with a giant bastard sword.
GM
1. We were short on players for the beginning of Reign of Winter, so the two PC's (a human inquisitor and a ratfolk witch) hire a brave warrior (Warren Peace), a sweetheart adept (Ada Nother), and a sneaky kobold fighter. They also made friends with a Half-Orc Rogue.
They get beaten up and almost killed by the bad guy death priest, thanks to his freezing skeletons and bad die rolls. Rather than inflict the dreaded TPK on the party, I did the classic "capture then for later." The witch's familiar, the rogue and the adept escape. The familiar (under the player's control) convinces and leads the the two NPC's back to the base.
In the basementThe PC's improvise clubs and light wooden shields out of barrels. The kobold fighter sets up a Macguyver rig and kills the last remaining skeleton with an apple barrel swing. The NPC warrior keeps the trapdoor open, slips on the ladder rung and lands on his crotch.
The party, reunited, proceeds to beat the crap out of the Death priest. After he goes down to fusillade of crossbow bolts and homemeade clubs, the party beats him to a bloody pulp. "You see that!" the inquisitor says, "You should have done that to us!"
Bad die rolls don't have to be a disaster, but a opportunity for great fun.
2. A superhero game. Doctor Lovenut, an alchemically mutant squirrel, stole one of the vending machines (the whole thing!) from a player character's factory and buried it in his front lawn. This character was so popular another player character based his character off of Docter Lovenut. Even made acorn cluster grenades.