Edit in JSFiddle

$( document ).ready(function() {
    $('#showComment').on('click',function(){
        $('#facebookComment').show(function(){
            //remove the comment to see the comment box appear
            //FB.XFBML.parse();
        });
    });
});

<div id="fb-root"></div>
<script>(function(d, s, id) {
  var js, fjs = d.getElementsByTagName(s)[0];
  if (d.getElementById(id)) return;
  js = d.createElement(s); js.id = id;
  js.src = "//connect.facebook.net/es_LA/all.js#xfbml=1&appId=651565091531466";
  fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));</script>

<div id="facebookComment">
<div class="fb-comments" data-href="http://example.com/comments" data-numposts="5"></div>
</div>
<button id="showComment">Show comment</button>

#facebookComment {
    display:none;
}