A very sensitive issue for both staff travelling as non-rev as well as for cabin crew.
I am now non-flying, working for a UK based airline and have also worked for BA on the ground for some years in the past. I have always adhered to
1) the rules for staff/duty travel which dictates your conduct on board, e.g. order of service (eg. if your first meal/wine choice isn't available etc......), not disclosing to other pax that you are staff etc etc
2) common sense. I always treat others as I would like to be treated. So why oh why I have to be treated differently because I happen to work for the same company as the crew is beyond me. Conversely, why oh why would I treat the crew with disrespect just because I work for the same company?
Apart from the obvious point 1) above I have never understood why the service experienced by staff or duty travellers should be any different on board, I have even heard fare paying pax commenting on the fact that they have noticed how much better or worse they have seen staff being treated as well as how they have noticed how staff travellers have been behaving less than professionally on board.
I have been treated like scum in First Class on BA (my wife was in tears at the end of the journey by the rudeness of the purser - but we still just smiled and made no comments to offend), and I have been treated like a king in Economy - but I would really prefer to just be treated like all the other pax in a courteous and professional manner. No special favours or snide remarks just standard service 'by the book'.
I will always make sure that crew are treated with the utmost respect they deserve and I would hope they will treat me in the same manner when ever I have to fly on duty or on staff travel.