I would have to say that the worst driving experience had to be Cairo, Egypt. I rarely get nervous when riding with someone from a foreign country but the lack of, or total ignoring of the traffic rules, scared me. Two lanes roads became four lane roads. Stop signs became "suggestions" and one way streets were ignored.
It was very similar in Shanghai, China. The rules were followed a bit more closely but the numbers of cyclists and pedestrians who completely ignored any rules made me a bit nervous. I sure wouldn't want to drive there.