hey Dennis pretty good reaction you gave. Mine would be the same, or 'no'. The important thing i think is to react as coolly as possible.
But it's hard not to get thrown off guard.
I haven't had much succes in passing ... used to be better, about 10 years ago I also dressed in boy mode and looked convincing for my age, now what most people see is just 'butch' ... and I get people calling me madam everywhere still. In some situations it's impossible not to just respond as they expect. (correcting people is pointless. My pre-T voice is too girly). But I'm training myself to simply ignore them as if I really don't have a clue they could be talking to me, until they address me the right way, or in a neutral way.
Cindi, that's a hard situation to deal with. Good you were able to use the insurance and then leave the company.
Though quite a few people already know what's going on, for some practical reasons I'm still using my female name at work for now. As
... I know I'll have the full support of my boss, but I am starting to realise more what kind of nasty reactions can come from other people. I work for the catholic church, and do temp work in nursing homes as well. The temp work will be easier, I can just avoid working in places where people won't respect me. Anyway, the old people in the nursing homes are the only people who consistently address me as 'boy'.

a lot of the time I work in psychogeriatric wards where the people won't remember who I am. There are quite a lot of queer people among the staff in most places, I've noticed, so there won't be many colleagues who will treat me badly, I think.
...then there's the church... in spite of the enraging, stupid comments that the churhc in Rome produces, ... I love working there, and have found a rare community of truly christian kind people...
within a small subcommunity of my church, I have met an ally. there's a mass for international students, I sing in the choir. Another member of the choir is also ftm!! we get along great, and it's much easier for both of us, to have someone around who understands and shares the same worldview.
the priest and parish board completely support me... but there are always conservative people who will have an issue with me... and church is also a place where people go for gossip, and I'll have to be careful with that. I'd hate to have to leave ...