I'd have to say that the worst one I've ever encountered was a basement that was finished by Harry Homeowner who wired the entire thing with lamp cord. No boxes at all, just nice little cutouts in the paneling with the devices screwed in place. Even though this looked to have been done in the late 1960's, he used two-wire receptacles. Frankly, I'm surprised that the place didn't burn to the ground.
This was before it became popular to use home inspectors, so the new owners were in for quite a shock when I had to give them the bad news.
Of course, the whole basement was fed from the oil burner circuit. That is the only reason that this issue even came to light. The service man for the furnace noticed several pieces of lamp cord leaving the disconnect switch and brought it to the homeowner's attention.
