There's a great passage in this account of meeting a troll face-to-face.
The victim confronts his tormentor, who breaks down and explains his actions:
I put my hand on his shoulder and asked him "Why?"
The Troll sat there for a moment and said "I don't know. I don't know. I'm sorry. It was like a game thing."
A game thing.
So, that's what it was...
This is a good example of the classic game criticism, that games teach bad behavior.