<?php

// ...

//delete all options
function my_plugin_uninstall_options() {
	global $wpdb;

	$users = $wpdb->get_col( 'SELECT `'. $wpdb->users.ID .'` FROM `'. $wpdb->users .'`' );
	foreach ( $users as $user_id )
		delete_user_option( $user_id, 'option_two' );

	delete_option( 'option_one' );
	delete_option( 'option_two' ); // it is used as a fallback
}

my_plugin_uninstall_options();

// ...

?>