The one time a DM used a vampire to dominated one of my characters, he order him to kill another party member
So I duly rolled my attack, critical fumbled, on the fumble table rolled friend-slayer (attack nearest ally), which was now the vampire, rolled to attack, got a critical hit and killed it.
There was a brief moment of silence then everyone collapsed in laughter.
Which was made worst when my character insisted he had thrown off the mental domination and intended the attack.