Interesting thread. I've never really understood why some people have a problem with either using the term 'Sir' or being addressed as 'Sir'.
Maybe its an age thing, and maybe it clearly shows a difference in attitudes between someone brought up in the '50 and '60's (like me) compared to later periods of upbringing.
I'm just an ordinary Joe who has no problem with either using the term or being addressed as Sir. To me it is just a respectful, polite and entirely appropriate formal address to be used in the professional avaiation world we enjoy.
I've had Captains who have said "Don't call me Sir, my name's John..." Fine! from then on he's John, but until such time, to me he is Sir or Captain.
During my early despatch days (Dan-Air, ahhhh!) we were dealing with many ex-RAF pilots, some of whom had seen action in Lancasters - now they really were gods, especially to am impressionable young man!
Even now, you go out to turnround an European airline, and the chances are that the CSM will be calling you sir!
Sure, you work with and get to know many pilots who become good colleagues, then its first-name terms all round, but until then, strangers will remain Sir or Captain in formal address.
Engineers always were and always will be scaley-backs to me (affectionately known as!) but they are a special breed who deserve every respect for the fantastic job they do, often in the most arduous of conditions. For me, the Line Engineer is 'Sir' with a capital 'S' (As in Sir Geraint!)