other.rb

module Kernel
  def other
    o = []
    ObjectSpace.each_object{|obj| o << obj unless (o==self)}
    o
  end
end

class Teapot
  
  def me
    puts "I am this teapot: #{self}"
  end
  
  def not_me
    puts "I am not: #{other.join(',')}"
  end
  
end

teapot = Teapot.new
teapot.me
teapot.not_me