A way to personally nickname someone

[osfanbuff63]

I wish it would be possible to personally nick someone. What I mean by that is you could do /pnick <player> <text> and when /msging someone if you typed the text you entered it would give the text entered/their username priority. However, this would either show up in chat to only you or not at all. And it wouldn't be visible to other players (unless they had a permission maybe?)