How could a polite AND sincere conversation with an agent be wrong? It is just not that frequent to occur and gate agents recognize a friendly passenger. For them, it is a welcome change compared to all those demanding, and sometimes plaine rude passengers. On many occcasions I have been in the F/BF check-in line behind another passenger and had to make the joke to the better half: and you think I am a difficult person...

The real question should/could be: do you behave differently when flying in confirmed BF?

I myself can't answer this question any more since I now travel F/BF exclusively and think I am still the same person regarding to attitude. However, I do admit that in the past I scored many upgrades by the described "flirting". My strategy was to check-in with a male agent, speak with an accent and wear fluorescent colours. At least, the gate agent will vaguely remember you (more than the just average flyer), which worked in many, many cases. I had no status or whatsoever and was always flying the most inexpensive tickets.

So, I don't think it can possibly be wrong, but it must be a sincere conversation.