Remember the reason behind interviewers asking this question of candidates, and remember that they ask this question of all candidates. Try not to define your self-esteem by a weakness. Admitting your weakness to the interviewers is not so they can privately tear you apart over it. It helps to look at your selected weakness objectively.
Also, the interviewers will remember your methods of self-improvement rather than your weakness itself. You will likely see positive cues from them like supportive body language because interviewers love hearing about candidates actively working on themselves.
The interviewers are there to accept an individual who will continue to grow and learn, so demonstrate that you are that shining individual.