Thank you everyone for your reply. I feel much better now :)

Hi,
I want to remove someone from my interview data. It's because the person doesn't fill the requirements. You may think how this could have happened if I am the one choosing the participants... well, my research was rejected from few social services, and I thought that interviewing a lecturer in similar field would be beneficial. I e-mailed him, sent him the questions, and he said he would participate. But when the interview started he had nothing to talk about because he hadn't had any experience in this, and doesn't know any one who had! We talked about the matter for ten minutes, it was mostly him being arrogant and finding faults in my research and terminology...like for example, me using an american word, which is not used in English law. How wrong was he and I explained it him that it is used in English law and in what circumstances, and he got even meaner. I had enough, I thanked him politely and left. I wish I had more courage to stand up and say what I thought of him.

So my question is, should I inform him in writing that I am not going to include his interview in my research?