But who cares that it's a bad question. The point is that it was asked and you should either answer it, evade it skilfully, or find a tactful way to decline to answer.
The poster asserted that "100% of developers have an answer" to this question. We're discussing why some developers may not have a good or immediate answer, and why the question is not as good as he asserts.
Well, I don't know about how good this question is, but it is one that gets asked a lot. And I do still think that 100% of developers have an answer, because I am sure every developer has felt proud about something he did, no matter the size, otherwise why would they still be a developer?