As long as the person makes an honest mistake about calling someone a mam or sir, and they are not that gender. I don't see the problem, now if someone is deliberately calling them a different sex to be mean. Then yeah your fine to be a bit pissed off... Honestly I don't care what someone identifies as. The only times it bothers me a bit is when it comes to like sports. That South Park episode did it best where they had Macho Man Randy Savage identifying as a woman and just beating the hell out of the women. The episode was hilarious but it did raise some interesting questions.