I've been thinking about this question for awhile, now, and the answer is one that kind of surprised me:
The thing about myself that I am most proud of is the fact that I don't know how bread is made. I know that you take wheat, and throw it into a machine, and it turns into dough, and you bake that. But that's it. That's the extent of my knowledge on the subject of bread making. I don't know what the machine is, or how it works, and I don't know if you have to mix more ingredients in, or if it's fine as it is or whatever.
Now, I'm sure that the question is going through your head: "Wait, how can the thing you're most proud of be something you don't know?"
Well, it's because I'm alive. I don't know the process to make one of the staples of a human diet, and I'm alive, and chances are, I'm going to continue to live for a good while. Five hundred years ago, I would be dead if I didn't know how to make my own bread. My ignorance of such a simple process is my own personal 'screw you' to the natural process, to nature that demands such ignorance be met with the culling of the weak.
And yet, here I am.
So that's the thing I'm most proud of in my life.