Every candidate knows how to answer this question: Just pick a theoretical weakness and magically transform that flaw into a strength in disguise!

For example: "My biggest weakness is getting so absorbed in my work that I lose all track of time. Every day I look up and realize everyone has gone home! I know I should be more aware of the clock, but when I love what I'm doing I just can't think of anything else."

So your "biggest weakness" is that you'll put in more hours than everyone else? Great...

A better approach is to choose an actual weakness, but one you're working to improve. Share what you're doing to overcome that weakness. No one is perfect, but showing you're willing to honestly self-assess and then seek ways to improve comes pretty darned close.