Person A has known Person B for several years but doesn't know Person B's parents. Person A hears that Person B's mother has died. Person A doesn't contact Person B as they haven't seen each other for a while and aren't really in touch but get on well if they bump into each other. They used to be friends and go out and socialise but life went in different directions.
Is person A being unreasonable not to have got in touch (YANBU)
or
Is person B being unreasonable to be annoyed that they didn't (YABU)