When I was one of the people running the London Bisexual Group, so oooh fifteen or so years ago, they'd be forty or so people turn up each week including five to ten new people.
One week, someone came back for their second time and was most miffed that I couldn't remember his name from the previous week. So miffed in fact that they declined – no, 'refused' would be a better word – to remind me, and continued to do so ever afterwards. I soon stopped bothering to ask.
Today, I saw them again, with someone rather more sensible and now I know.
Not that I'm likely to remember, mind.