Worst problem: My own crappy attitude.
Why it was the worst: I have none of the obvious attributes you read about in psych texts and self-help. I'm not a pessimist, I don't dwell on the past, I don't get angry, etc. This issue was very difficult to see clearly.
How I solved it:
First, I realised being too future-oriented was problematic. While I didn't dwell on the past, I was discounting my present situation far too much, perhaps pathologically.
Secondly, I realised my lack of an emotional response was due to a deeper emotional problem: resentment. Resentment is an interesting emotion. Resentment just kind of hangs out in the background, rather than making you do anything dramatic. Resentment seeks to eliminate its object, rather than harm it. This means it's usually expressed in withdrawal. If you're very anti-social and unemotional, you're probably suffering from resentment.
Thirdly, I realised I overlook a lot of my own negativity because I enjoy it so much. It's the source of my humour. I have a tendency to revel in it. Somebody getting in my way as I walk down the street will unleash a burst of perfectly enjoyable mental vitriol. I love a good rant. I didn't think this was a problem because it wasn't marked by strong emotion. It gave me a sense of superiority. I felt it was part of my personality.
I had all of these insights while reading a book on Tibetan 7-point Mind Training (specifically Traleg Kyabgon's The Practice of Lojong) but they are not necessarily contained in that book. It was really my own reaction to the radical altruism of the text that let me dig deep and find these problems. I did apply the book's idea of keeping watch on my own thoughts and letting go of the ones I now recognised as negative before they had a chance to snowball. This is an effective technique. You just have to develop a counter-habit of thinking, "Oh, I'm doing it again."
Outcome: I no longer hate people.
It sounds like me, except that catching myself isn't really the problem. The problem is that I haven't found a way to ask my internal Grinch to stop once I've noticed it at work. It doesn't help that I have a tendency to be hard on myself and go meta. I'll notice that I'm being negative, get annoyed about it, get annoyed about me unproductively getting annoyed and giving myself negative reinforcement for noticing, and then I will have built up enough bad affect that whatever other lines of thought I have will be poisoned too. I realize the self fulfilling ...
EDIT: No one was doing what the post suggests, so I accepted an idea from one of the comments, and embedded my response in a comment, not the post itself
I'd like to ask this question to you, and I'll respond it myself as well.
What Is The Worst Problem You've Ever Encountered and Solved? And the One You Didn't, Yet!
Some prior considerations:
1) I mean "problem" in a very general sense, it could be a math problem, an existential problem, a social problem, an akrasia problem, a disease problem etc...
2) I'd like people to give informative/didactic responses. Try not only to state the facts, but also to help someone who'd encounter similar situations to be able to deal with them.
3) When talking about the one you didn't, give enough specifics that someone would actually be able to help you.
The general idea is to teach people how to Win by example, taking in consideration all the shortcomings of biases etc...
Well, that is all. One solved, one not yet solved. State your own issues and help others here. Someone else's rationality is always welcome.