usernames = "mrmactout
angusmactout
elsbethmactout
sgtmacfuzz
mrsmactoffy
professordunkopf
ferociousness1983
littleness1983
hungryness1983".split("\n")

require 'rubygems'
require 'twitter'

list_slug = "<my list slug>"
user = "<my username>"
password = "<my password>"
throttle = 10 # seconds to wait inbetween calls to twitter

puts "Adding #{usernames.size} users to #{list_slug}"

httpauth = Twitter::HTTPAuth.new(user, password)

client = Twitter::Base.new(httpauth)
usernames.sort!
usernames.reverse!
usernames.each do |username|
  begin
    client.list_add_member(user,list_slug, username)
    sleep(throttle)
  rescue Twitter::General
    puts "General error for #{username}"
  rescue Twitter::Unavailable
    sleep(throttle)
    client.list_add_member(user, list_slug, username)
  end
end