<?php //the_category(', '); ?>

<?php //lets try get_the_terms_list instead

echo get_the_term_list($post->ID, 'category');  ?>

<?php

//try one using NOT IN

add_filter('list_terms_exclusions','my_list_terms_exclusions');
   function my_list_terms_exclusions($args) {
      $where = " AND t.term_id  NOT IN ('12')";

        return $where;
   }

//try 2 slightly different

add_filter( 'list_terms_exclusions', 'my_list_terms_exclusions' );
function my_list_terms_exclusions( $exclusions ) {

     $exclude = "12,28";
     $exclusions .=  "AND t.term_id != " . $exclude . " ";

       return $exclusions;
}


//try 3 (found on net)


function my_list_terms_exclusions( $exclusions, $args ){

    // IDs of terms to be excluded
    $exclude = "28,12"; //  IDs OF YOUR TERMS

    // Generation of exclusion SQL code
    $exterms = wp_parse_id_list( $exclude );
    foreach ( $exterms as $exterm ) {
            if ( empty($exclusions) )
                    $exclusions = ' AND ( t.term_id <> ' . intval($exterm) . ' ';
            else
                    $exclusions .= ' AND t.term_id <> ' . intval($exterm) . ' ';
    }

    // Closing bracket
    if ( !empty($exclusions) )
        $exclusions .= ')';

    // Return our SQL statement
    return $exclusions;
}

// Finally hook up our filter
add_filter( 'list_terms_exclusions', 'my_list_terms_exclusions');