What's a good answer to the question "What's your biggest fault"?

Alison's Contribution:

To me an answer is only good if it's the truth for you. 

So I would start with "My biggest fault that I recognise today is "... You might also want to say "The biggest fault I had when I was younger was ..., and I overcame that by "... 

I think this is one of those questions where the non verbal behaviour will be viewed as much as your response.