private_init.rb

class Foo
  private

  def initialize
    puts "calling initialize"
  end
end

foo = Foo.new

remove_initialize.rb

class Foo
  class << self
    undef_method :initialize
  end
end

class Bar < Foo
end

bar = Bar.new
puts bar.inspect

unset_ivar_methods.rb

class Foo
  class << self
    undef_method :instance_variable_set
    undef_method :instance_variable_get
  end
end

class Bar < Foo
  attr_accessor :baz
end

bar = Bar.new
bar.baz = "hello"
puts bar.baz