Years ago, in a campaign before the Defenders, Piratecat had a player who was a TERRIBLE paladin. Foul mouthed, rude and abusive (and that was the character), he was Lawful Good only in his dreams. PC had spoken to him on numerous occasions about the shaky ground he was treading.
Finally, the straw that broke the camel's paladinhood was him cursing out an enemy in language most foul. PC turned to the player and said "So what does your fighter do next?"
The player, a little slow on the uptake said "No, wait, I don't play a fighter. I'm a pala...."
It was a beautiful moment.