<p>is it unacceptable to ask the interviewer how i should address him?</p>
<p>It is perfectly acceptable.</p>
<p>[Don’t take me at my words, I’m just a fellow applicant this year.]</p>
<p>I can’t see why it wouldn’t be unacceptable.</p>
<p>Instead of asking, another option is to play it safe and use the interviewers title (Dr. Mr. Ms.) and last name. If the interviewer wants less formality, at that point he/she can say, “Please call me Joe”.</p>
<p>In a business setting, it’s perfectly acceptable. I’m sure it’s true for an interview as well. When in doubt, go MORE formal than less.</p>