Which question(s) do you have the hardest time answering truthfully?

I answer all of them truthfully, and some bluntly with what I believe they need to hear. Gets me in trouble somedays. But I wish people would do the same. One of my many bosses asked me what I thought about him, I said I couldn't think of a worse example of how someone could do the job. Everyone else always said good. A few hours later he came back and asked me why I said that. So I told him because it's what he needed to hear, there are things that if he changes them and works towards to improve. I listed the problems my group was having with him and how to fix what it was. A couple of weeks later he thanked me for being honest with him and how he noticed a change in the way people acted around him.