How to limit access to certain users for those who have "administer users" permission
The administer users permission is a VERY powerful permission and you shouldn't give this permission anyone that you don't trust. Otherwise, the users with that permission can do all nasty things. For example:


They can manage fields on user accounts at admin/config/people/accounts/fields
They can manage permissions and grant/revoke users including themselves other permissions at admin/people/permissions
They can add/cancel/edit users including admins!


Conclusion: Never, ever give this permission to ANYONE!

There are a few modules that let users granularly administer other users. One of them is the Administer Users by Role. Although, its latest version for Drupal 7 requires to give this mighty permission to the users, but there's a patch, which I also contributed, at this issue page. With this patch, you don't need to give 'administer users' permission to the users and still allow them to administer other users.

There are also other related modules, but I cannot tell anything about them since I don't use them:

Subuser


  This module allows users to be given the permission to create subusers. The subusers may then be automatically assigned a role or roles. The parent of the subusers then has the ability to manager the users they have created.


Role Delegation


  This module allows site administrators to grant some roles the authority to assign selected roles to users, without them needing the administer permissions permission.