Originally we put the leaving messages in as a debugging aid, but it turns out they’re quite handy, so we decided to keep them until we introduce something like Periscope’s bubbles.
However some broadcasters feel insulted every time somebody leaves, so we decided to make them light-hearted random messages. Many of them are Aussie vernacular.
You can’t choose your own as that seems a bit too open to abuse.
We will probably allow you to configure them off in future, as they can tend to become annoying after a while. (We’re actually surprised people have liked them as much as they have so far.)