Add user report button in message thread.

user-report-message-thread.php

/**
 * Add block/unblock button on single message thread.
 */
function buddydev_show_user_report_button_on_message_thread() {

	// only message involving single user can be blocked.
	if ( ! function_exists( 'bpmts_report_button' ) || ! bp_is_my_profile() ) {
		return;
	}

	global $thread_template;

	if ( ! $thread_template ) {
		return;
	}

	$recipients = wp_list_pluck( $thread_template->thread->recipients, 'user_id' );

	if ( empty( $recipients ) ) {
		return;
	}

	$my_id    = get_current_user_id();
	$other_id = 0;
	foreach ( $recipients as $user_id ) {
		if ( $user_id != $my_id ) {
			$other_id = $user_id;
			break;
		}
	}

	if ( ! $other_id ) {
		return;
	}

	bpmts_report_button(
		array(
			'item_id'    => $other_id,
			'item_type'  => 'user',
			'context'    => 'bp_message_screen',
			'context_id' => bp_displayed_user_id(),
		)
	);
}

add_action( 'bp_after_message_thread_recipients', 'buddydev_show_user_report_button_on_message_thread' );