I was so proud of my new Barbarian Patriarch, level 88 and 34k defense.
In fact, he was made solely to see how much defense I could pack onto one character. I had seen Fury druids fail to kill him, Zealots too.
I was letting a friend take shots at him for the heck of it, and went up to get a Dew. It took a lot longer than expected. When I got back, I saw the death screen, and the only explanation was thus:
My friend, who was perfectly capable of handling any enemy around me, suddenly had to go, and had killed my mercenary as a joke.
A pack of Fallen strayed close to me, and decided they would try their hand at killing me.
They, after what must have been an eternity, managed to.