If you're completely honest, you may be kicking yourself in the butt. If you say you don't have one, you're obviously lying. This is a horrible question and one that politicians have become masters at answering. They say things like "I'm perhaps too committed to my work and don't spend enough time with my family." Oh, there's a fireable offense. I've even heard "I think I'm too good at my job, it can often make people jealous." Please, let's keep our feet on the ground. If you're asked this question, give a small, work-related flaw that you're working hard to improve. Example: "I've been told I occasionally focus on details and miss the bigger picture, so I've been spending time laying out the complete project every day to see my overall progress."