Online fandom stuff generally, whether Buffista or otherwise, mostly has invented contexts. These days I can say 'was talking to someone online about' without it getting too weird. When it comes to actual friends from the internet, though, these were usually met 'through another friend' - including The Girl, whose origin story is still not known to everyone in my life. Although I'm getting better at being honest about it. (Most fun moment ever: a few years ago, when I had a birthday party, and my new flatmate encountered twenty Bronzers descending on his living room. He was very good about it.)
Of course, that hasn't kept me from dropping hints to new kewl people I meet, in wild hopes that they might already be a buffista.
Not quite as good, but back in May, after sitting next to a friend at uni and going out for post-class drinks with her for six months, I learnt she was a fandom type. While her fandom was not my fandom, we knew each other's communities and had online people in common. She's the person who encouraged me to come back here and get posty (I think she herself was once a lurker here). Seriously awesome experience, that, when real life and online worlds collide unexpectedly.