real_private_method.rb

class A
  using(Module.new do
    refine A do
      def private_hello
        puts 'Hello, real private method!'
      end
    end
  end)

  def public_hello
    private_hello
  end
end

A.new.public_hello                        # => Hello, real private method!
A.new.private_hello rescue p $!           # => NoMethodError
A.new.__send__ :private_hello rescue p $! # => NoMethodError