Normally, when flying on a return ticket, I would present the airline with the passport that lets me into the destination country during check-in. This will sometimes result in showing two different passports (depending on whetever I am returning) with the same return ticket. However, quite obviously, this theoretically allows the airline to deduce that I am a multinational, and which two countries exactly am I citizen of.
Let's assume I didn't want the airline to know. What would be my course of action? Should I just avoid booking return tickets? Do you know any other tricks?
Edit: for the purposes of this question, let's assume I don't care if governments know or find out that I am a multinational. Just the airline.