Be cautious to prevent fire, theft and ChinaNET police.

Here's how to noindex a single post in wordpress without install any plugin or edit robots.txt file

1. open http://your-site.com/wp-admin/theme-editor.php, and choose to edit the header.php
2. add this line after a bunch of <meta> tags:
   <?php if (in_array($post->ID, array('2323', '2424', '2525'))) {echo '<meta name="robots" content="noindex">';} ; ?>
   In the above example we block wordpress posts with id 2323, 2424 and 2525.
3. Open Google Webmaster tool 1 or 2, and remove your search record &amp' cache from Google