function disable_comments_post_types_support() {
    $post_types = get_post_types();
    foreach ($post_types as $post_type) {
        if(post_type_supports($post_type, 'comments')) {
            remove_post_type_support($post_type, 'comments');
            remove_post_type_support($post_type, 'trackbacks');
        }
    }
}
add_action('admin_init', 'disable_comments_post_types_support');

function disable_comments_status() {
    return false;
}
add_filter('comments_open', 'disable_comments_status', 20, 2);
add_filter('pings_open', 'disable_comments_status', 20, 2);