bp_activity_remove_user_favorite( int $activity_id, int $user_id )

function bp_activity_remove_user_favorite( $activity_id, $user_id = 0 ) {

	// Fallback to logged in user if no user_id is passed.
	if ( empty( $user_id ) ) {
		$user_id = bp_loggedin_user_id();
	}

	$my_favs = bp_get_user_meta( $user_id, 'bp_favorite_activities', true );
	$my_favs = array_flip( (array) $my_favs );

	// Bail if the user has not previously favorited the item.
	if ( ! isset( $my_favs[ $activity_id ] ) ) {
		return false;
	}

	// Remove the fav from the user's favs.
	unset( $my_favs[$activity_id] );
	$my_favs = array_unique( array_flip( $my_favs ) );

	// Update the total number of users who have favorited this activity.
	$fav_count = bp_activity_get_meta( $activity_id, 'favorite_count' );

	// Update the users who have favorited this activity.
	$users = bp_activity_get_meta( $activity_id, 'bp_favorite_users', true );
	if ( empty( $users ) || ! is_array( $users ) ) {
		$users = array();
	}

	if ( in_array( $user_id, $users ) ) {
		$pos = array_search( $user_id, $users );
		unset( $users[ $pos ] );
	}

	// Update activity meta
	bp_activity_update_meta( $activity_id, 'bp_favorite_users', array_unique( $users ) );

	if ( ! empty( $fav_count ) ) {

		// Deduct from total favorites.
		if ( bp_activity_update_meta( $activity_id, 'favorite_count', (int) $fav_count - 1 ) ) {

			// Update users favorites.
			if ( bp_update_user_meta( $user_id, 'bp_favorite_activities', $my_favs ) ) {

				/**
				 * Fires if bp_update_user_meta() is successful and before returning a true value for success.
				 *
				 * @since BuddyPress 1.2.1
				 *
				 * @param int $activity_id ID of the activity item being unfavorited.
				 * @param int $user_id     ID of the user doing the unfavoriting.
				 */
				do_action( 'bp_activity_remove_user_favorite', $activity_id, $user_id );

				// Success.
				return true;

			// Error updating.
			} else {
				return false;
			}

		// Error updating favorite count.
		} else {
			return false;
		}

	// Error getting favorite count.
	} else {
		return false;
	}
}