selfish.rb

class Foo
  attr_reader :name
  def initialize(name)
    @name = name
  end

  def method_missing(name, *args, &block)
    return super unless name.to_s =~ /^go_/
    puts "Defining #{name}"
    method = lambda { puts "hey #{@name}@#{object_id}, #{name.to_s.tr '_', ' '}" }
    self.class.send :define_method, name, method
    method.call
  end
end

tony = Foo.new "tony"
tony.go_fish
tony.go_tiger

phil = Foo.new "phil"
phil.go_fish
phil.go_tiger

phil.go_to_school
tony.go_to_school

# Defining go_fish
# hey tony@2156971300, go fish
# Defining go_tiger
# hey tony@2156971300, go tiger
# hey phil@2156970160, go fish
# hey phil@2156970160, go tiger
# Defining go_to_school
# hey phil@2156970160, go to school
# hey tony@2156971300, go to school