If I walk alone and accidentally meet my wife's friend but I do not greet her, my wife will angry to me if she know about it, because in my place if we do not greet (at least with sign) someone who we know, it's considered as not polite.I think people are different. because even in the above situations you mentioned I would still get annoyed and feel as if "what business does that guy have talking with my wife, sure he may known her from somewhere in the past" but that's exactly that, the past, she's not his relation in anyway, so what business does he have coming up to my wife like that. He doesn't need to approach her, it was unnecessary for him to approach her.
That's what would be going through my mind, and if you kept doing it I would get annoyed and tell you stop approaching my wife cos you have no business talking to her any more, even if I'm there. People are different I guess.
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