Some great thread drift here! But back to the original ....
I finally found the time to watch the first episode and so watched it in the context of having read this thread first. My overriding thought regarding how QFIs and students referred to each other was whether or not due respect was shown in both directions and I felt that it was, as it was some 40+ years ago when I was at Valley. Back then it would have been disrespectful not to call your QFI 'sir' as that was the protocol of the time. Now, if the protocol is to call everyone 'mate' then so be it and, perhaps, to call ones Flt Lt QFI 'sir' may actually be disrespectful. I am still in contact with some of my QFIs from training days and we are long term friends. I am also in contact with some of the students from my first instructional tour almost 30 years ago and, again, we are friends.
When we started IOT at Cranwell (we were all Pilot Officers) the College Warrant Officer, in his first address to the course, said "Gentlemen, while you are here I will call you sir and you will call me sir. The difference is that you will mean it". It was said with the sardonic sense of humour that few other than RAF Regiment SNCOs have, and we all had the greatest respect for him for the rest of the course.