First you have to add a server of your choice to your favorites.

Second you have to join the server from your favorites and wait until it says "WAITING FOR HOST" in the middle of the screen and "Ready" On the bottom left corner of your screen. When you get to that screen spam the ESC key as fast as you can until you get kicked out to the main menu.

Then quickly join back to the same server.

When you join the game you need to move backward and you should see a copy of your self.

Then proceed to killing your duplicated person.

Lastly proceed to gathering your duplicated items.