In case you don't know, your ping is your connection to the server, high ping = bad, low ping = good. Add /ping so we can flex our ms to other players, its nice to be able to use it ingame and not have to go back to the server list. And it'd be useful to /ping (username) someone before fighting them so you wouldn't have to lose a fight due to ping difference. Ex: Prevents losing a fight to someone because they have 300 ping and are just lagging around getting sketchy hits during the whole fight.
This would be useful. We do have a /ping command though; whenever you do /ping you get a message saying "Pong!" back.
Actually, I know there are many plugins on bukkit for this...but I actually coded this for practice. So if he wants to have a custom plugin for it, I made one :P
