What negative trait or quality in a person do you find attractive?

Something that I believe others would find to be a negative trait or personality is a person with a sense of dark and morbid humour. I tend to use dark humour a lot more than I should and sometimes have to be pretty careful around who I say it. Having friends who can take in jest with the things I say without any repercussions is great, otherwise they wouldn't last that long as friends!

What do you consider a negative trait, quality, factor, and that you find attractive?