Safe Report Comments

This plugin gives your visitors the possibility to report a comment as inappropriate. After a set threshold is reached the comment is put into moderation where the moderator can decide whether or not he want to approve the comment or not. If a comment is approved by a moderator it will not be auto-moderated again while still counting the amount of reports.

Customizations

By default this script should hook in just fine in most existing themes as it attaches itsself after the comment-reply link via the comment_reply_link filter.
In case this does not work out you can place the flagging link manually by defining no_autostart_safe_report_comments in your themes’ functions.php file and initializing the class via $safe_report_comments = new Safe_Report_Comments(false);.

Here is an example of a custom setup via functions.php and placing the link comments callback function.

In functions.php:

//flag comments plugin included in themes' functions.php - disable plugin.
define( 'no_autostart_safe_report_comments', true );
include_once( 'replace-with-path-to/safe-report-comments/safe-report-comments.php');
// make sure not to auto-attach to comment reply link
$safe_report_comments = new Safe_Report_Comments(false);

// change link layout to have a pipe prepended
add_filter( 'safe_report_comments_flagging_link', 'adjust_flagging_link' );
function adjust_flagging_link( $link ) {
    return ' | ' . $link;
}

// adjust the text to "Report abuse" rather than "Report comment"
add_filter( 'safe_report_comments_flagging_link_text', 'adjust_flagging_text' );
function adjust_flagging_text( $text ) {
    return 'Report abuse';
}

In your custom comment callback function used by wp_list_comments: https://codex.wordpress.org/Template_Tags/wp_list_comments place the following action which will print the link.

<?php do_action( 'comment_report_abuse_link' ); ?> 

A possible callback function could look like this:

function mytheme_comment($comment, $args, $depth) {
    $GLOBALS['comment'] = $comment; ?>
    <li <?php comment_class(); ?> id="li-comment-<?php comment_ID() ?>">
        <div id="comment-<?php comment_ID(); ?>">
            <div class="comment-author vcard">
                <?php echo get_avatar($comment,$size='48',$default='<path_to_url>' ); ?>
                <?php printf(__('<cite class="fn">%s</cite> <span class="says">says:</span>'), get_comment_author_link()) ?>
            </div>
            <?php if ($comment->comment_approved == '0') : ?>
            <em><?php _e('Your comment is awaiting moderation.') ?></em>
            <br />
        <?php endif; ?>
        <div class="comment-meta commentmetadata"><a href="<?php echo htmlspecialchars( get_comment_link( $comment->comment_ID ) ) ?>"><?php printf(__('%1$s at %2$s'), get_comment_date(),  get_comment_time()) ?></a><?php edit_comment_link(__('(Edit)'),'    ','') ?></div>

        <?php comment_text() ?>

        <div class="reply">
            <?php comment_reply_link(array_merge( $args, array('depth' => $depth, 'max_depth' => $args['max_depth']))) ?>
        </div>
        <div class="report-abuse">
            <?php do_action( 'comment_report_abuse_link' ); ?>
        </div>
    </div>
    <?php
}

Furthermore there are various actions and filters within the script to allow easy alteration of implemented behavior. Please see inline documentation.

Known issues

Automatic mode implementation currently does not work with threaded comments in the last level of threading. As the script attaches itself to the comment_reply which is not displayed once the maximum threading level is reached the abuse link is missing at this point. As a workaround set the threading level higher than the likely amount of threading depth.