We're all ignorant about something, Dr. Bill. We all learned our language initially (and at a level that we may even call instinctive) from listening to others using it, in the earliest stages, mostly our parents. If they had used may instead of can in the context of asking permission they wouldn't have had to berate us about our so-called misuse of the terms later. I think that treating a simple request to interrupt one's privacy for the purpose of getting what may well be critical information as a discourtesy is indicative of a greater discourtesy. Think of people's intent and don't hold them to standards that have slipped years ago. I could accept regarding "Hey pops! Tell me something." as being discourteous, but not "Can I ask you a question?"