At Readings for a book launch on Friday (the second that week) I was trying to get close to the action and found myself stuck in a long aisle with no chance of seeing anything. I passed a woman who smiled at me and looked familiar, and assuming she was a graduate student in my school (there are lots and lots) I made a cheery remark about what a terrible place it was for a booklaunch. (And it is, in its logistics, though I love that they are willing to have academic book launches there.) You can't see or hear the action very well, and if you are a customer wanting to browse those sections for an hour, it's impossible. Anyway I explained all this to the poor girl, then went back around and up another aisle and found some people I knew. During the launch speech, I looked over to the cash register where the wine was being served, and sure enough, there she was, obviously an employee. Well, she may also be a graduate student. But I did feel foolish. But have learned that it only makes it worse to go and apologise for my rudeness: viz. "I'm sorry I was rude about your workplace: I thought you smiled at me and I wrongly assumed I should have known who you were — but didn't." And even worse to start explaining about the whole face-blindness syndrome.
Also, what I want to know is this: how many times is it acceptable to refer to your own work when launching a book by someone else? Not that many, I would have said. I have just been invited to do my first launch speech, in December, so my mind is much occupied by the genre.