So if you would do /warp pvpworld you would have pvp automagically on and there wouldn't be any way of turning it off.
You would keep anything you can kill, so if you could kill someone with full gem you could have all items he dropped.
Nukes and all dirty tricks you can think of to kill someone else would be allowed.
Basically it would be "If you can kill it you can keep it." and "If it's not banned it's allowed." free for all pvp.
P.S. It's not cheating because that one thing you did do isn't on the list of things not to do...