Can I enable / extend a module, but mark all included / extended methods as private?

Include and then explicitly make all included methods private?

class A
  include B
  private *B.instance_methods
  extend B
  class << self
    private *B.instance_methods
  end
end

You can Moduleadd a monkey patch private_includeand private_extend:

class Module
  def private_include *modules
    class_eval do
      self.send(:include, *modules)
      modules.each do |mod|
        self.send(:private, *mod.instance_methods)
      end
    end
  end

  def private_extend *modules
    singleton = class << self; self end
    singleton.instance_eval do
      self.send(:include, *modules)
      modules.each do |mod|
        self.send(:private, *mod.instance_methods)
      end
    end
  end
end