My brother once asked my husband what his salary was, because brother was in the process of applying for jobs. Husband didn't want to share what he earned, but did give a general indication of what was useful in their field of work. My brother kept pressing, why didn't husband share it? It's not like he would post it on facebook or something! Husband said that it was private.
Brother started mailing that he didn't understand why he didn't tell him, they were so close, it was something friends would do, and that he didn't like husbands attitude.
Two momths later when I went out to dinner with brother for his graduation, brother started interrogating me as for why husband didn't share it, And regurgitated all the arguments.
Appareantly, if he can't umderstand why people have certain boumdaries, he feels he doesn't have to respect them.