You work in an office where there are often - up to and including a dozen times a week - top surgeries for female to male trans men. You know this, I would hope.
You should really, really not be saying the word 'tranny' extremely loudly, while insisting that a male-to-female trans person recently in the news was a man. And you should almost certainly not be arguing with someone who is currently accompanying someone who is getting top surgery done about this. If you don't know that this is offensive, you should NOT be working there.
[I am not only out-of-state but out of country atm, and I don't know if this is something I can actually complain about, or how to go about it, or if it's even worth it, but I at least needed to vent because I don't want to bother my friend or his mother about this just after the surgery.]