So a few days ago someone asked me if I knew <femalename>.  She was referring to another trans guy that I know in person, and it took me a moment to realize who she was talking about.  When I did I asked, "Wait, do you mean <malename>?  Yeah, I lived with him for a while." (tried to put emphasis on him)  She told me that she had met him as <femalename> and commented on how "she's becoming a man."
I mean, maybe she just doesn't know better, but I was too exhausted to explain how disrespectful that is and it's been bugging me since.  I should have said something.