bbPress.org

ok, the answer is somewhere in this function

function bbp_title( $title = '', $sep = '»', $seplocation = '' ) {

	// Title array
	$new_title = array();

	/** Archives **************************************************************/

	// Forum Archive
	if ( bbp_is_forum_archive() ) {
		$new_title['text'] = bbp_get_forum_archive_title();

	// Topic Archive
	} elseif ( bbp_is_topic_archive() ) {
		$new_title['text'] = bbp_get_topic_archive_title();

	/** Edit ******************************************************************/

	// Forum edit page
	} elseif ( bbp_is_forum_edit() ) {
		$new_title['text']   = bbp_get_forum_title();
		$new_title['format'] = esc_attr__( 'Forum Edit: %s', 'bbpress' );

	// Topic edit page
	} elseif ( bbp_is_topic_edit() ) {
		$new_title['text']   = bbp_get_topic_title();
		$new_title['format'] = esc_attr__( 'Topic Edit: %s', 'bbpress' );

	// Reply edit page
	} elseif ( bbp_is_reply_edit() ) {
		$new_title['text']   = bbp_get_reply_title();
		$new_title['format'] = esc_attr__( 'Reply Edit: %s', 'bbpress' );

	// Topic tag edit page
	} elseif ( bbp_is_topic_tag_edit() ) {
		$new_title['text']   = bbp_get_topic_tag_name();
		$new_title['format'] = esc_attr__( 'Topic Tag Edit: %s', 'bbpress' );

	/** Singles ***************************************************************/

	// Forum page
	} elseif ( bbp_is_single_forum() ) {
		$new_title['text']   = bbp_get_forum_title();
		$new_title['format'] = esc_attr__( 'Forum: %s', 'bbpress' );

	// Topic page
	} elseif ( bbp_is_single_topic() ) {
		$new_title['text']   = bbp_get_topic_title();
		$new_title['format'] = esc_attr__( 'Topic: %s', 'bbpress' );

	// Replies
	} elseif ( bbp_is_single_reply() ) {
		$new_title['text']   = bbp_get_reply_title();

	// Topic tag page
	} elseif ( bbp_is_topic_tag() || get_query_var( 'bbp_topic_tag' ) ) {
		$new_title['text']   = bbp_get_topic_tag_name();
		$new_title['format'] = esc_attr__( 'Topic Tag: %s', 'bbpress' );

	/** Users *****************************************************************/

	// Profile page
	} elseif ( bbp_is_single_user() ) {

		// User is viewing their own profile
		if ( bbp_is_user_home() ) {
			$new_title['text'] = esc_attr_x( 'Your', 'User viewing his/her own profile', 'bbpress' );

		// User is viewing someone else's profile (so use their display name)
		} else {
			$new_title['text'] = sprintf( esc_attr_x( "%s's", 'User viewing another users profile', 'bbpress' ), get_userdata( bbp_get_user_id() )->display_name );
		}

		// User topics created
		if ( bbp_is_single_user_topics() ) {
			$new_title['format'] = esc_attr__( "%s Topics",        'bbpress' );

		// User rueplies created
		} elseif ( bbp_is_single_user_replies() ) {
			$new_title['format'] = esc_attr__( "%s Replies",       'bbpress' );

		// User favorites
		} elseif ( bbp_is_favorites() ) {
			$new_title['format'] = esc_attr__( "%s Favorites",     'bbpress' );

		// User subscriptions
		} elseif ( bbp_is_subscriptions() ) {
			$new_title['format'] = esc_attr__( "%s Subscriptions", 'bbpress' );

		// User "home"
		} else {
			$new_title['format'] = esc_attr__( "%s Profile",       'bbpress' );
		}

	// Profile edit page
	} elseif ( bbp_is_single_user_edit() ) {

		// Current user
		if ( bbp_is_user_home_edit() ) {
			$new_title['text']   = esc_attr__( 'Edit Your Profile', 'bbpress' );

		// Other user
		} else {
			$new_title['text']   = get_userdata( bbp_get_user_id() )->display_name;
			$new_title['format'] = esc_attr__( "Edit %s's Profile", 'bbpress' );
		}

	/** Views *****************************************************************/

	// Views
	} elseif ( bbp_is_single_view() ) {
		$new_title['text']   = bbp_get_view_title();
		$new_title['format'] = esc_attr__( 'View: %s', 'bbpress' );

	/** Search ****************************************************************/

	// Search
	} elseif ( bbp_is_search() ) {
		$new_title['text'] = bbp_get_search_title();
	}

	// This filter is deprecated. Use 'bbp_before_title_parse_args' instead.
	$new_title = apply_filters( 'bbp_raw_title_array', $new_title );

	// Set title array defaults
	$new_title = bbp_parse_args( $new_title, array(
		'text'   => $title,
		'format' => '%s'
	), 'title' );

	// Get the formatted raw title
	$new_title = sprintf( $new_title['format'], $new_title['text'] );

	// Filter the raw title
	$new_title = apply_filters( 'bbp_raw_title', $new_title, $sep, $seplocation );

	// Compare new title with original title
	if ( $new_title === $title )
		return $title;

	// Temporary separator, for accurate flipping, if necessary
	$t_sep  = '%WP_TITILE_SEP%';
	$prefix = '';

	if ( !empty( $new_title ) )
		$prefix = " $sep ";

	// sep on right, so reverse the order
	if ( 'right' === $seplocation ) {
		$new_title_array = array_reverse( explode( $t_sep, $new_title ) );
		$new_title       = implode( " $sep ", $new_title_array ) . $prefix;

	// sep on left, do not reverse
	} else {
		$new_title_array = explode( $t_sep, $new_title );
		$new_title       = $prefix . implode( " $sep ", $new_title_array );
	}

	// Filter and return
	return apply_filters( 'bbp_title', $new_title, $sep, $seplocation );
}

a filter such as

function amend_title () {
	if ( bbp_is_single_forum() ) {
		$new_title['text']   = 'YA book forum' ;
		$new_title['format'] = esc_attr__( 'YA book Forum', 'bbpress' );
		}
 return $new_title;
}
add_filter('bbp_before_title_parse_args', 'amend_title' );

should sort it but doesn’t, and I’m too tired to work out why 🙂

Over to you !