This is very useful if you have lots of people posting pieces of code in your comments. No longer will it disappear!

 
// This will occur when the comment is postedfunction plc_comment_post( $incoming_comment ) { 
// convert everything in a comment to display literally$incoming_comment['comment_content'] = htmlspecialchars($incoming_comment['comment_content']); 
// the one exception is single quotes, which cannot be #039; because WordPress marks it as spam$incoming_comment['comment_content'] = str_replace( "'", ''', $incoming_comment['comment_content'] );
return( $incoming_comment );
}
// This will occur before a comment is displayed
function plc_comment_display( $comment_to_display ) {
// Put the single quotes back in
$comment_to_display = str_replace( ''', "'", $comment_to_display ); 
 
return $comment_to_display; 
} 
add_filter( 'preprocess_comment', 'plc_comment_post', '', 1); 
add_filter( 'comment_text', 'plc_comment_display', '', 1); 
add_filter( 'comment_text_rss', 'plc_comment_display', '', 1); 
add_filter( 'comment_excerpt', 'plc_comment_display', '', 1);