Dealing with someone who asks many questions during presentations
You are not obligated to accept somebody disrupting your talks, particularly when the questions are off-topic and when much of the audience appears to be disapproving.  The basic solution is to act as a moderator for your own talk.


For questions during your talk that you find disruptive, a simple solution is simply to say, in a calm and gentle voice, something like:


  I'm going to defer that question for now.  We can come back to it at the end.

During a question period, if a person is dominating the discussion, you can say something like:


  I think some other people may want to ask questions as well, so I'm going to ask you to hold your questions for a bit while we hear from others.



The key here is to be firm, gentle, and impartial.  Your voice should make it clear that it's not about this particular questioner or about you being defensive, just about keeping on topic.

After you say something like this, most people will leave the question and let you come back to it later.  If the questioner does not, simply repeat yourself, remaining as calm and unruffled as you can, and then move on.  If the person continues to be disruptive after that point, it will be clear that they are making an unusually large problem, and others are likely to help intervene.