Sometimes I have to help friends or family with their PC, wlan etc. One time I had to help one because their wlan were open and neighbours were using it. I remembered someone creating a genius solution for this.
I know this is old but it deserve to be bumped a little. There was a guy who were fed up by neighbours who leached on his wlan, not wanting to lock it he thought of a more fun way to torture his neighbour. He created a split on his wlan so when his neighbour connected he got on an own system. And in that system were a script which turns every image upside down! So when his neighbour surfed around everything seemed ok except the images that were upside down.
I love this one. You can read about it here.