Office Girl Question:

It feels like a trap. If you answer honestly, you're admitting to something that could potentially turn off an employer. If you say "I have no weaknesses. I am perfect," the employer will know you are either a liar or totally lacking in self-awareness, and dismiss you outright. You have to say something.
Think of an actual weakness, something that isn't an essential requirement for the job, and explain how you became aware of it and are working on improving upon it. This shows that you are reflective, willing to learn, and striving to get better.

Don't say: I'm a workaholic and/or a perfectionist.