gistfile1.rbx

class String
  def method_missing(method, *args, &block)
    if method.to_s =~ /is_(.*?)\?/
      self.downcase == $1
    else
      raise NoMethodError, "Undefined method '#{method}' for #{self.inspect}"
    end
  end
end

"bob".is_bob?   # => true
"jim".is_tom?   # => false
"karl".foobar   # => 
# ~> -:6:in `method_missing': Undefined method 'foobar' for "karl" (NoMethodError)
# ~> 	from -:13