I would not be surprised if some FA's turn their backs to it.... I have flown with some people who just do not have a backbones, contradicting what I said before about me not knowing anyone who would allow it, unfortunately, I guess I do. I have flown with other FA's that come up to me when I work first class and ask me if a passenger can sit in FC if seats are available. "Hello!, NO!" Why would they even lead this person to believe there might be a possibility! Tell them "NO" from the get go! I firmly believe that first class is just that, FIRST CLASS. I don't always have "first class" people sitting up there, but I do my best, with what is available to me, to make it first class. Sad to say, some may not appreciate it, but that will not detour me from doing what I can to make it that way. This does not include just the service, but keeping those people out of those seats and their bags out of those bins for which they do not belong! And asking such questions when they board, "if seats are available, can I just take one?" Or just taking a seat there when you are not ticketed is definitely not "first class".