Grab the gem.

gem 'cinch_joker'

And add the joker to your cinch bot as a plugin:

bot = Cinch::Bot.new do
  configure do |c|
    c.server          = "irc.freenode.net"
    c.plugins.plugins = [
      Cinch::Plugins::Joker
    ]
  end
end

compactcode: !joke
bot: He who smiles in a crisis has found someone to blame.