I had just started working at a new job. My new boss was transgender. Im honestly not sure whats considered the appropriate way to say this, so if this offends someone, please correct me and let me know how I can say it correctly in the future: My boss had the voice of a man over 50.
At one point my boss called over to me to ask a question, and I replied, yes, sir. Things got real quiet, and I realized what I had done. I apologized, but no one said anything. Ten minutes later I received a long email instructing me in no uncertain terms to never use that word again.
I was grateful to have the opportunity to work there and we developed a good relationship after that. I still wish I could have been better prepared for that; I feel really bad about it to this day.