What a strange way of expressing something. I understand the same thing MrPernickety.
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YankeeHi Alex
Additional context might have an impact on my intrerpretation, but to me the comment in bold seems sarcastic, and seems to suggest that A is the last person that person B would expect to notice and/or care about whether or not B is upset.
In the broader context, was A responsible for the fact that B was upset?
Hi, Amy