public function addMention($username)
    {
        if (
            $mentioned = $this->getService('repos:people.person')->find(array('username' => $username))
        ) {
            $this->mentions->insert($mentioned);

            if ($this->_mixer->isSubscribable() && !$this->_mixer->subscribed($mentioned)) {
                $this->_mixer->addSubscriber($mentioned);
            }

            return $this;
        } else {
            $this->invalidateUsername($username);

            return;
        }
    }