Actually you still owe him respect even if he wasn't your instructor's instructor.
Actually I take issue with this statement. He needs to EARN respect no matter what or who he thinks he is. Now in a formal setting you have to respect the rank... to a point. However when that person abuses his position you owe him nothing.
I understand many feel that way. However, in Korean culture, respect is automatically given.
This makes sense if you think about it. There are many situations were respect is automatically given. In the military for example, if a general walks by everyone stands at attention and salutes. If someone disagrees with an order of a superior rank, there is a respectful procedure to follow to have that addressed.
Many people disagree with calls made by the referee during a match. Which shows the proper attitude, continuing to be respectful to the referee even if you disagree with the call, or to take the attitude that the referee has now disrespected you, that he/she failed to EARN your respect?
Often times we do not know or understand the reasons given for our seniors actions. I can tell you of many instances both in the martial arts and outside the martial arts where I did not feel like listening, where I was upset at what was being asked of me, only to later find out that my objections were without merit. Had I flew off the handle and taken the screw you route, then everything would have been made worse. I have come to realize that in situations such as these, it is a test of your discipline and training on how you handle the situation.
Put another way, when we were teenagers, we rebelled against our parents and felt they could do no right as far as we were concerned, only to learn later that they our parents actually had our best interests in mind when they told us to not smoke, to do our homework, not stay out late or drink at the prom or whatever else. At the time it felt like an invasion on our person (who are they to tell us what to do?), but was it really, in hindsight? In any event, it is best in these situations, to automatically give respect, rather than take the position that respect is "earned".