Fallout 3. I was doing the assassination mission for Mr Crowly in Underworld. "You've got to shoot them in the head" it was called. I told him I wasn't going to kill the three non-ghoul haters. He attacked me. Next thing I know the whole town is after me and I die several times from the Mr Gutsy before realising I need heavier firepower. So I travel back to where I stashed my Fatman, retrieve it, and head back to Underworld. I then try several times to kill that bloody robot. Eventually, I think it was on my 7th or 8th attempt, I nuke the robot and kill off any hostiles. As I'm standing victorious I literary yell out "Hell yeah! I killed them" Before realising I've pretty much committed genocide. "Oh shit. I killed them". The only people left were Carol, Tulip, and three randoms. I felt awful. I also spent time trying to talk more to Tulip. I was always drawn to her, I just wanted to her what she had to say. Which wasn't much. But she was still my favorite character (wow that sounds so otaku-ish).