For me in China, it's driving. Driving is an exercise that challenges every single notion of whatever seems organized and predictable and regular. It challenges every bit of patience and self-control. It is wonderful to be able to drive because it does give you a lot of freedom, but I still hire drivers and take cabs into the city sometimes, due to traffic and parking headaches. If you don't know where you're going and you get lost, it is a looooooong time to get straightened out.
There are 22 million people and some 6 million cars. Beijing does have fantastic roads, considering they were built when there were hardly any cars on the streets, and Beijing does have actual rules and regulations for safe driving (I know, I did take the test and know exactly what to do if I'm in an accident and my passenger has become somehow disemboweled--I get a bowl and place it over my friend's stomach so I can contain the intestines). Beijingers often drive the way you might walk or ride a bike--at variable speeds (a freeway can have people driving 90+ mph and 35 mph--in the same lane...and you can back up if you miss an exit).
The horn is essential and you must use it all. the. time. Back home, the horn, aside from that friendly "beep" reminding you that the light is green, signifies a pretty big misstep--changing lanes without looking, cutting someone off, etc. Here, the horn is applied when you come up behind someone, when you are turning, when you see someone else turning, when you see a bike/scooter/pedestrian, when you are passing, when you are being passed...you get the idea. Using your blinker is optional, and rather pointless, since no one will pay attention to it. Turning may be accomplished whenever you think of it, from whatever lane you happen to be in. Not sure what to do? Just stop and think about it. It's OK if you're in the middle of a lane. Or an intersection. Or a driveway. We can drive around you because using the oncoming lane is always a viable option.
In America we spend an inordinate amount of time thinking about other people. Don't take too much, there might be others. Don't stand so close, the other person might feel uncomfortable. Defensive driving is all about thinking about the other person. In China, it is all about me. If there is an inch between me and the car in front of me, then a car will definitely swerve in, forcing me to brake (hard). It's OK, because it's my responsibility to get out of his way. If I'm turning onto a road, I don't have to look, because it's the responsibility of the oncoming car to see me turning and slow down or get out of the way. It's taken 3 years, but I've finally figured out the rules and expectations (which have nothing to do with the driving exam questions I learned).
There has been NOTHING living overseas that has inspired more ill feelings toward my host country or put me in a sweaty fit than driving. I never was a tense or frustrated driver, but here....grrrrr. Never in my life have I choked back so much profanity! It amuses me to think that something so silly as how people drive sparks such a reaction--I think it's because when I'm in the car, I'm going somewhere and it's then that I miss the ability to be efficient and get so much done on an outing, ala America. EVERYTHING takes so long and EVERYWHERE we go, it's in a monstrous crowd, whether it's on a freeway or in a shop. When in Rome, though...so I do what I need to, because driving by "my" rules won't get my anywhere--literally. Watch out!