This is a common question, but don't dwell on it. The interviewer is looking for a job related answer, more like "what bothers you about your job or the people you work with?" If you dig deep and think of what really bothers you, you will find that it's other people and their ideas, right? But don't tell the interviewer that, you can be more clever than that.

"It bothers me the most when other people I work with don't meet their deadlines or deliver what they promise."