How to disable sortable headers in Admin theme tables
Found the answer by reading this fine article

https://knackforge.com/blog/karalmax/drupal-7-creating-drupal-style-tables-paging-sorting-and-filter

"If you do not want a particular column to be sortable, do not specify the 'field' parameter for its header."

My headers array is now simply

   $headers = array(
      array('data' =&gt; 'UID'),
      array('data' =&gt; 'Username'),
      array('data' =&gt; 'Given Name'),
      array('data' =&gt; 'Family Name'),
      array('data' =&gt; 'Email Address')
    );


with no 'field' value specified, and the clickable headers have disappeared.