Billy Day is a holiday that happens on the 18th of every month. On this day, every living creature is named Billy. No last names, no middle names; everyone's full name is Billy. Why is this, you may ask? Life gets a bit more interesting when you can't just use a shortcut (like someone's name) to refer to whom you're talking to/about. You'll have to do what you can to make it clear to people which "Billy" you're referring to when you say "Billy."
It's been asked before, "What about someone whose name is already Billy?" Their name is still Billy on Billy Day.

1. The default beliefs installed when you were a child.

2. An unexamined position you absorbed from your environment growing up.