Traffic. I've driven in NYC, Boston, LA, Chicago, Cleveland, Philadelphia, Baltimore, DC., Dallas, and Houston. Nothing compares to Athens, Greece.
Got to Athens about 5PM on a Sunday. It went OK until I got to the first rotary. The traffic was stalled. Drivers were sitting on top of their cars talking. One set of drivers was involved in some sort of game. Some kids were playing in between the cars. We didn't move an inch until about 8PM. Fortunately, there were some Greeks that knew a little English and could explain that this was normal.
Had a friend in Athens who was a professor at the University of Athens. The hotel clerk found out I knew someone in Athens and spent all day tracking him down for us. Refused to accept a tip. Thought it was great that we knew someone in Athens. But, he did let us know that it took so long because he was at U. Athens Medical School, not U Athens. Told us our friend would be there to pick us up at 5:00. I looked for his car. Never saw it. Instead, a bus stopped, and he jumped off the bus. Why would someone with a brand new car ride to bus to pick us up and leave his brand new VW at home? We rode to his apartment in a taxi.
Turns out that his wife, whom we also knew, was within a week or so of delivering her first child. They had a parking place within three blocks of their apartment, and they didn't want to give it up while she was pregnant. They wanted to be able to get to the car in a hurry if she went into labor. So, having a parking place, they didn't drive their car in the last month of her pregnancy.
Now, we can talk about traffic and parking problems.