This might not be a real question, my apologies, but I'm pretty sure it will make your doomsday scenario enjoyment work a little.
My company act as a contractor for a larger company. We need to plug various devices on their internal network. They have a (security) limitation that prevents us from plugging a switch or router to any ethernet jack they have available. (why does that even make sense?)
Now since we do need more than one jack, we asked them to lift that restriction for us. They told us that they did. When we arrived on site, we plugged a single switch (very basic stuff) to the jack, and then the whole world came to an end. They experienced major network failure and received logs of "duplicate ips, duplicate macs" and such and the whole plant came to a grinding halt.
Of course we are accused of being responsible for this mess. My coworkers and I totaly fail to see how this could happen. Do you have any idea of why a single switch can crash a whole network?