All my bad PT experiences just involve people trying to take over roles that they really shouldn't. Some choice quotes...

"Torren, tank for us while we find a new one."
"But I've only got DD equipment. My defense is really low."
"Don't worry, we'll keep you alive."

or...

"Theoriginalg, please stop voking mobs. You're not the puller."
"Im just levaling up wile we wait"
"You're aggroing everything in sight! Our mages can't keep up with you!"
"Not my problam lololololol"
*booted*

or...

"Ummm, why aren't you tanking?"
"I hate tanking"
"...You're a NIN"
"So?"

and my favorite...

"We need to stop pulling ITs. This isn't working. People keep dying."
"We're doing fine"
"Ok, only we're not. Our tank keeps dying. We have downtime every battle."
"If u dont like it u can leave"
*gets booted*