But I thought of something the other day. While I was making a new build and I was summoning for every boss (because why not), I was always a bit disheartened when my teammate when I was fighting the taurus demon had fully upgraded lightning gear and one shotted the boss. It made me feel cheated. And from that I realized the worst possible troll.
Here it is:
If you were summoned to someone's game who was obviously new on their first playthrough at one of the very early bosses. Then once you confirmed this dropping him all duped stuff. Like 99 of each boss soul, 99 humanity, lightning weapons, fully upgraded armor, and then DCed out.
Would be the worst possible thing in dark souls.