Lavender.
Ruby basically wanted to free Lucifer from Hell. In order to do that, she needed me. As it turns out, the demon blood issue I have is because of that reason. I was supposed to be some...apocalypse starting idiot or something.
She lied to me. Said that using my abilities would help me protect my family. Eventually it got to the point where...I did some...questionable things. It was, admittedly, somewhat my fault for agreeing to the suggestions she made, but fact of the matter was that she manipulated and used me to get where she wanted. She even got me addicted to drinking demon blood a substance that made me neglect everyone I cared about and eventually...
I murdered. Not people, but demons. I guess some of them are considered people around here.
My point is that I'm supposed to be a smart guy. I'm not gonna brag and say that I'm the smartest ever, but I'd like to think that I've got at least a good amount of sense in my head. If she was able to take someone like me and turn them into that, there's no telling what she might do to anyone else who gives her a way in.