Well, unless the other someone specifically allows you to. I was once playing as Capt. Firefox, and Firefox as Jack Flash, and we both said fine, you can be me. Of course, this is communication between two close friends.

However, as was said, cloning or pretending to be someone without their permission (ESPECIALLY someone who everyone knows and loves, like MaGoo) is a very bad thing. It only confuses people as to who's who when they find out there's more than one of something. Besides that, you will eventually be caught, much faster thanks to IP publishing on server hosts. Although someone who can remember IPs off the top of their head has my respect straight off.

Last note: I only used MaGoo's name because he was the first person I thought of who's famous on the JCF and is famous on JJ2. That's all. We love the rest of you too.

Good god, I hate writing stuff that makes sense. I'm so bad at it.