At the moment, the list of parameters available under the list_authors tag is limited. In particular, the only author you are allowed to exclude from the list is the author whose login is "admin" (the "exclude_admin" parameter). Now, aren't we all told that we shouldn't have "admin" as our super-user login?... So, if you've followed this advice, you're not going to be able to exclude the super-user's name from the list_authors list.
So the list_authors tag should be enhanced to enable you to exclude any author you like (or dislike!)