Board Thread:General Discussion/@comment-12838149-20161206122839/@comment-25739558-20161206132057

Generally, bureaucrats can only be demoted by means of community consensus. Your best course of action in this case is to create a public demotion thread for that user and leave it up for a week or so. If the community vote to demote said bureaucrat is successful, let Staff know via Special:Contact and they will remove the rights of that user.

Some further reading on the subject:
 * User blog:Sannse/Why Staff Don't Remove Bad Admins
 * User blog:Mira Laime/How to Deal With a Bad Bureaucrat