Nasty Celebs I've met:
JLS - 'We haven't got the time for you, we're going for dinner.'
Jacquie McQueen off Hollyoaks - Don't know her name in real life and I don't want to. Said hello to her and she gave me a dirty look. So I said back 'Eee, why've you got a face like a smacked arse?!' and she didn't know what to say.
I don't think being busy on a way to dinner, and not having time for fans makes someone nasty, though.
Also, Maybe Jacquie McQueen didn't hear your "hello" and actually gave you a questioning look? I've hear reports about her, that she is actually quite lovely.