I hate this question because unless you phrase it just right you sound like either A) you are evading the question B)are outright lying, or C) are too stupid to recognize that this a test of whether you can give smart but BS answers. Alternatively you can be an idiot and actually tell them a real weakness that probably DOES effect your job Ex. "I am racially predjudiced and have trouble getting to work on time." and which can outright disqualify you. At best, this seems like a lose-lose question.