config.rb

require_relative 'Settings'

module BadBehaviour
    class Settings
        include DefaultSettings

        extend self # make all methods class methods
    end
end

Settings.rb

module BadBehaviour
  module DefaultSettings
    def strict
      false
    end

    def verbose
      false
    end
  end
end

shell output

$ irb
irb(main):001:0> require './config'
TypeError: wrong argument type Class (expected Module)
	from /home/mathrick/Dev/bad-behaviour/ruby/config.rb:58:in `extend'
	from /home/mathrick/Dev/bad-behaviour/ruby/config.rb:58:in `<class:Settings>'
	from /home/mathrick/Dev/bad-behaviour/ruby/config.rb:4:in `<module:BadBehaviour>'
	from /home/mathrick/Dev/bad-behaviour/ruby/config.rb:3:in `<top (required)>'
	from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
	from /usr/lib/ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
	from (irb):1
	from /usr/bin/irb:12:in `<main>'
irb(main):002:0>