The reason it is annoying for people who are experienced is that generally they are looking for jobs where they get to work on difficult and interesting problem

The reason it is annoying for people who are experienced is that generally they are looking for jobs where they get to work on difficult and interesting problems. Being asked such a simple question might indicate that you are interviewing for a position you won't want. I'd personally be very tempted to answer the whiteboard question and immediately explain that I'm not interested in a job that consists only of writing trivial implementations and ask if they can give examples of real problems they face which are non-trivial. I have actually had one interviewee ask me such a question, although not in response to a simple test or question of my own. This impressed me, although I get the impression that most interviewers would not appreciate this in a similar way to how they do not appreciate candidates that find their fizz-buzz test annoying. An interview is not a one way test. It is a two way test where the employer can also fail.