Quick advices

you shouldn’t need sslverify => false:

$cwbadges = wp_remote_get('https://coderwall.com/'.$this->username.'.json', array( 'sslverify' => false));

You should also html escape the data coming from coderwall before using it in HTML:

foreach($cwbadges->badges as $badge){
            $badges_string.='<img class="cwbtip" src="'.$badge->badge.'"
              alt="'.$badge->name.'" title="'.$badge->description.'" />';
          }
          $badges_string.='</div>';

Also, you should apply some filtering on the username and endorsement before using them. Not a big deal, just good practices.

Thanks for the awesome work anyway 🙂