Evil campaign.
I was playing a Brd/Rog/Clr-with-Trickery-domain, heading for some custom Doppelganger-style PrC. Master of disguise and impersonation, that sort of thing.
And in the character creation process, I'd decided that he wasn't just going to have certain roles he used a lot... he was actually going to have multiple personalities.
I was playing a selfish, self-interested, subtle evil. Unfortunately, I discovered everyone else was playing over-the-top, twirl-the-moustache, kick-puppies-and-make-sandwiches-out-of-them, cartoony evil.
We were assigned a task by an evil mastermind. Hamm (the character in his bard personality) noted that he had some contacts he wanted to check with for information... and he would send someone more suited to an assault on a church. He went off, talked to his contacts, and then let the Grey personality (the evil cleric) to the fore. He rendesvoused with the rest of the group moments after the attack on the church began, and took up a backstop role, preventing anyone escaping to get help.
Once the fight was over, he entered the building to suggest to the characters bathing in the blood of the slain, etc, etc, that perhaps now was not the time, and they should accomplish the task and leave before the Watch arrived.
He was seized, and a dagger held to his throat, with a demand that he stop this farce and admit he was Hamm, or be killed.
I sent an email to the DM - "What should I do? Grey doesn't believe he's Hamm... should I play him to character, or just drop the whole multiple personality idea to avoid derailing the game?"
"Your call," she replied.
So I decided To hell with it, and played him as he was originally envisioned - he claimed that Hamm had sent him to help, and they were being ridiculous.
So they cut his throat.
-Hyp.