Was reminded of this by a post about the difficulty of creating high level encounters.
So, years ago, near the beginning of the time I seriously began playing D&D, I was a wizard in a campaign set in the Forgotten Realms. Mostly it centred around the troubles that a small town was having, and all the various calamities brought on by local goblin tribes and the like. We started out at level 1, and clawed our way through the campaign to find out that everything had been orchestrated by a White Dragon that had recently moved into the area, and had begun conducting experiments around freezing the villagers and the like.
As any brave party would do, we go to confront the white dragon in his lair as the final, epic, set piece to cap the whole campaign off. We've been building up to this moment the whole way through, and are now ready for the absolutely classic "party vs dragon" scenario. Now, I've got Phantasmal Killer in my 4th level spell slot, because I wasn't that experienced, and hey, Save or Die spells are always nice to have, right?
We charge in, knowing the dragon is in his lair, and somehow (DM fiat or invis, maybe) get a little bit of the drop on it. Winning initiative, I figured what the hell, and let fly with the Phantasmal Killer right as I got within range of the dragon. Natural 1, Natural 1. Boom. Campaign is over, and only one player even got to act in the final climactic battle.
The DM and the other players are looking at me like "Seriously? You just ruined all the awesome!". Suffice to say, the players were not happy, and the DM was
not happy. He'd gone to all this work to custom build an appropriate white dragon as a challenge for our party, setting him up in the campaign world, leaving little hints around, and one action in a surprise round later, all the work he put in went bye bye.
End result was it being strongly hinted that my playing a wizard again wasn't in my best interests.