Thank you for the responses. I think that I'll probably do some variation of what FTMax suggested (#3). I facilitate meetings for the graduate students in my program (usually weekly), and will make an announcement there (or maybe send an email if people don't show up to the meeting), something along the lines of:
"While most of you have been and continue to be really awesome about using the correct pronouns and generally treating me like anyone else, there are some who continue to habitually misgender me, and even make off-handed comments about how I identify and express myself. I really didn't want to be demanding about it because I recognize that it takes effort on your part. However, at this point, it's been over nine months, and this is no longer an issue of simple misgendering but of being incredibly disrespectful. I can't interact with people who refuse to show the same level of respect that I show to them so, if this persists, I will be distancing myself from those who are very knowingly being disrespectful - and I will not mask the cause of this break from the professors or other graduate students, nor will I be the one to initiate reconciliation later on if they want it."
It's probably harsh, but at this point, I am hating coming in to work (which I otherwise love), and that's unacceptable. If the people doing this keep it up after that, I'll go to my department chair and request to change offices, and tell them exactly why.
@Suzi, I also tend to be very forgiving but at this point, it's too much. I've only ever misgendered one person *once,* and I felt terrible. They were non-binary so, I think they took it very well but I still felt like the biggest jerk ever. Thankfully, I've never had a problem misgendering anyone else.
@Alexis: I actually *despise* the term transsexual, and would never use it for myself or anyone else unless explicitly told to do so, but that's me and my perspective on life, and people are totally entitled to their own opinions, and to identify however they're most comfortable.