1.) There was this one time where I told myself "Glork can't possibly be scum
again
," and so did not seriously pursue him as a Day One lynch in ScumChat. And then he turned out to be scum. Since then, I have stuck true to the maxim that Glork must always be scum (which has proved invaluable).
2.) In a different game on ScumChat (on the same day as the one TrojH mentioned) with four players alive and going up against a SK and a Vigilante going against my scumbuddy TrojH, when in fact I could have forced a win by forcing a no-lynch (because TrojH also happened to be a scum Doctor who could self-protect), I instead placed the lynching vote upon him after being pressured by the other two players. That was a real slap-my-forehead moment. TrojH could not be nightkilled, and as long as we killed a Vigilante or SK the next night (which was guaranteed) he could also not be lynched so long as I didn't do anything stupid.
3.) On a completely different forum (which usually hosts 30-player or so games with 1 real-time-day deadlines, with two groups of 5 scum) I random voted one my partners on Day One (a Werebear in that game,
not
the Werebear in this forum), and at that particular forum, a random vote is enough to start a bandwagon that ends with a lynch. He was quickly run up and lynched solely because of my random vote. I got a few angry PMs from him afterwards.
The second day, I decided there was no way it would happen again, so I voted for another one of my partners: people apparently thought that was good enough, and he was then subsequently run up and lynched. I began to get angry PMs from both my partners.
As it happens, that game also had conversions: my third partner had apparantly been converted to the Witches by that point (which I was unaware of at the time), leaving me with one lone killing partner (since I was an evil Seer, and I was not allowed to kill). The witches had six players by that point (their evil Seer, their four killers, and my converted partner) against the Werebear's two players!
Funnily enough, I played my cards perfectly afterwards: I successfully used our conversion on one of the Witches, and through him, we determined almost all the roles in the game (since he had information from the opposing Evil Seer). He directed kills for the Witches behind the scenes while coordinating with us Werebears. Although I was eventually lynched, our conversion managed to pull off a spectacular win after my horribly botched opening.
I don't believe I have ever felt so guilty over a game than I did in that one.