My idea is that you would be able to solve this, just you and him.
Challeging Derp:
You may propose a challenge for somebody by a text command like: /challenge [derp] (or a simple one, like /x1 [derp]
Being Challenged by Herp:
The player who's being challenged would acept challenge by a text command like: /acptchallege [herp] ( or a simple one, like /acptx1 [herp])
If accepted, there would appear a simbol, maybe a skull or something, of the player who called for a challenge in the challenged player map and vice versa. So there you can go to the player location and solve your issues with him.
That's my idea, it's very simple, then please leave your opinion in the pool. Thanks
P.S.: I'm Brazilian, so sorry if there's any pathetic english grammatical mistake.
Thanks for compreension.
Hope you guys like it.
PedroIora