pocketmine\event\player\PlayerQuitEvent::setQuitMessage PHP Method

    public function setQuitMessage($quitMessage)
    {
        $this->quitMessage = $quitMessage;
    }

 public function onQuit(PlayerQuitEvent $event)
 {
     // Epic Fail
     $player = $event->getPlayer();
     if ($player->isOp()) {
         $event->setQuitMessage("|ScMCPE|" . $player->getDisplayName() . "[Ranked] est hors ligne!");
     } else {
         $event->setQuitMessage("|ScMCPE|" . $player->getDisplayName() . "est hors ligne!.");
     }
 }