thing.rb

class User < ActiveRecord::Base
  validate :only_superusers_can_do_foo

 private
   def superuser?
     if account == "Super User"
       true
     else
       false
     end
   end

   def only_superusers_can_do_foo
      if !superuser? 
         errors.add_to_base "Normal users can't do that!"
      end
   end

end