bp_get_activity_parent_user_id()

	function bp_get_activity_parent_user_id() {
		global $activities_template;

		// Bail if no activity on no item ID.
		if ( empty( $activities_template->activity ) || empty( $activities_template->activity->item_id ) ) {
			return false;
		}

		// Get the ID of the parent activity content.
		$parent_id = $activities_template->activity->item_id;

		// Bail if no parent item.
		if ( empty( $activities_template->activity_parents[ $parent_id ] ) ) {
			return false;
		}

		// Bail if no parent user ID.
		if ( empty( $activities_template->activity_parents[ $parent_id ]->user_id ) ) {
			return false;
		}

		$retval = $activities_template->activity_parents[ $parent_id ]->user_id;

		/**
		 * Filters the activity parent item's user ID.
		 *
		 * @since BuddyPress 1.7.0
		 *
		 * @param int $retval ID for the activity parent's user.
		 */
		return (int) apply_filters( 'bp_get_activity_parent_user_id', $retval );
	}