This happened to me once 2 years ago at Gatwick whilst flying with my partner to Copenhagen on Maersk.

Dressed smart casual and casually mentioning that I worked for ATC(i do really!), we asked nicely at check-in for an upgrade, but Mrs Check-in bit our heads off. By way of reprimand she then proceeded to tell us that as the flight was full, our perfectly legal hand luggage would have to go in the hold.

During resultant exchange of words about the hand luggage, the duty supervisor for Maersk (who had obviously been earwigging whilst talking to another colleague) butted in and said words to the effect of "Mrs Check-in was right, the flight is full so we'll put you in Business class so that you won't have any problem taking your bags on board and hopefully you'll make your connection. Have a nice flight". She then walked off leaving Mrs Check-in looking embarrassed and us in 2A and 2C!!!

I don't know who was more surprised- us or Mrs Check-in!!!