It is vitally important that you don't prepare for the talk. Ideally you should have no slides. Nor should you have any index cards with vital points written on them.
In a perfect world, you'll still be hacking on the code you're going to be presenting mere minutes before the tech meet starts. If that hacking is actually spent desperately trying (and failing) to implement the code needed for the lightning talk 'preface' to your talk (so you do it with a whiteboard and your audience's imaginations) then you get bonus points.
For more bonus points, consider heckling the guy who goes on before you, slowing him down and thus increasing your chances of missing your train home.
Then, for your presentation just plug the lapdog into the projector, fire up an emacs window and walk people through the code, starting with the relatively easy to understand 'top level' subroutine.
Enjoy the audience's expressions as you get to the really evil stuff you've abstacted away in helper methods which let you do stuff they didn't think was possible.
For further bonus points, have an 'aha!' moment on the train home which would probably have got your lightning talk demo working if you'd thought of it in time...
