You can just talk to them in your mind, they can think for you sometimes, you can ask them for advice or ask them to decide which movie you want to rent tonight. You can get into arguments with them, and you can have intelligent conversations with them.
You can't kill them.
They might slowly fade away in time... but... I don't know...
You can completely change into your imaginary friend. Sad I know.
Person #2- Um, okay...
For Muslims, is Allah.
For Jews, is Jehovah.
For Zaroastrians, is Ahura-Mazda.
A: A Five-year-old child doesn't insist that his imaginary friend is King of the Universe.