It seems there is no way to manually order users in a WordPress site. You can choose between some available options when using get_users or WP_User_Query and that’s it. There is even no filter to allow manipulation of ordering.

And I needed this for a site I was working on:

Enter Simple User Ordering – a plugin that I wrote which allows admins to manually ordered WordPress Users with a simple drag’n'drop.

User drag and drop feature in action

Check it on Github:

Interface is heavily influenced by Simple Page Ordering and the name honors it :)