I was in elementary school and was obsessed with the 'Log on to' dropdown box on Windows login screens, and how you could use the same credentials on any PC.
Somehow I managed to salvage an old computer and source myself a copy of the ISO and managed to setup an ADDS domain controller and join my mother's laptop to the domain.
I went and asked the IT guy for advice on doing a multi forest configuration and I think it blew his mind. Why did I want multi forest? Guess I was preoccupied with whether or not I could, and didn't stop to think if I should. : )