r-a-y

function my_member_username() {
    global $members_template;

    return $members_template->member->user_login;
}
add_filter( 'bp_member_name' , 'my_member_username' );

function my_bp_displayed_user_fullname() {
    global $bp;

    return $bp->displayed_user->userdata->user_login;
}
add_filter( 'bp_displayed_user_fullname' , 'my_bp_displayed_user_fullname' );

// the following function requires a core hack @ bp-activity/bp-activity-templatetags.php on line 578
// change:
// apply_filters( 'bp_get_member_name', $comment->user_fullname )
// to:
// apply_filters( 'bp_get_member_name', $comment->user_fullname, $comment )
function my_get_member_name($name, $comment) {
    return $comment->user_login;
}
add_filter( 'bp_get_member_name' , 'my_get_member_name', 1, 2 );

function my_bp_get_activity_action($action, $activity) {

    $displayed_user = bp_core_get_core_userdata( $activity->user_id );

    return str_replace( $displayed_user->display_name, $displayed_user->user_login, $action );

}
add_filter( 'bp_get_activity_action', 'my_bp_get_activity_action', 1, 2 );

function my_bp_get_the_topic_post_poster_name($name) {
    global $topic_template;

    return str_replace($topic_template->post->poster_name, $topic_template->post->poster_login, $name);
}
add_filter( 'bp_get_the_topic_post_poster_name' , 'my_bp_get_the_topic_post_poster_name' );

function my_bp_get_the_topic_last_poster_name($name) {
    global $forum_template;

    return str_replace($forum_template->topic->topic_last_poster_displayname, $forum_template->topic->topic_last_poster_login, $name);
}
add_filter( 'bp_get_the_topic_last_poster_name', 'my_bp_get_the_topic_last_poster_name' );