Mettā Stage 4: "Difficult Person"

Thinking about the fourth stage of Mettā meditation practice, which is traditionally said to have you focus on a "difficult person", I wonder: - Does the person have to be someone that you know personally? - Could you, for instance, focus on someone in the media or a celebrity (whom you don't know personally, but believe to be a "difficult person")? - Is it important that you have a personal connection with this person at this stage of practice? Thanks!