There are some things that can be gross or just super different from you own culture and thus hard to understand. Here are my thoughts on the matter.
When walking around you will notice that most of the locals clear their throat often and spit and make horrendous noises while at it. It is normal here. They say it is a residue of the old times as China has had a very strong agriculture until several decades ago. That people are “so accustomed to walking in the fields that they feel it is ok to spit anywhere” there has been some effort to root this habit out of the nation, like for the Olympics there were educational measures taken to make people quit it. Most of the younger generation find spitting as gross as westerners and there is a chance that the habit will eventually die out. Most likely the people who actually live on the countryside won´t care because they actually walk the fields where a little bit of spit does no harm.
Shanghai has the population of Finland x4 and I think that sometimes all the people have of their individuality is the sense of self. Like when you walk around and there are people making a bottle neck in some point the Finnish way is to politely wait until the bottle neck is over and then go. But the Chinese just walk ahead and barge through, it is like the faster you walk the busier you are. Chinese people are very good in looking at their phones and avoiding physical contact with the others at the same time and I cherish the slow driving skills of the bike or motor vehicle drivers, they very often can´t go fast and have to go forward at a snail’s pace because simply there is no room.
Also one thing that is not considered rude or not nearly as rude as elsewhere is staring. Chinese people shamelessly stare at you if they find you interesting and some might want to have their picture taken with you. I don´t mostly notice because I use the Finnish method of power walking -looking at your feet when you go.
One very interesting thing is the toilets. You know when you have to go you have to go. Most of the toilets are the squatting type with the toilet bowl at the floor level. There are some western toilets available but let that relief fool you. In my experience if the floor is wet it is not water. Mind you NOT water. Something else, you know what. Near the sinks yes but elsewhere, nopenopenope.
All the toilets usually have running water to wash your hands after but free toilet paper is a luxury, I strongly recommend having your own tissues with you. And all the toilets have a bin inside, it is for sanitary towels etc. but also for the toilet paper. You do not flush the TP here, it WILL block the toilet. (Exception for the rule is the dorm, the toilet hasn´t been clogged yet.)
Majority of the toilets smell like old pee but are fairly ok besides the wet floor and the smell. I think that the squatting type toilets are generally cleaner than the western ones. People don´t pay much attention to the toilet that they don´t have to clean.
My weirdest toilet experience has been one with the holes just next to each other, like a group toilet and one with partially open, low walls. The worst on was at a temple where the toilet building was outdoors and without window glasses, it was filled with countless of fat white spiders just hanging there in the ceiling. Had no trouble peeing there, I am afraid of spiders lol. When going out one good indicator to stop drinking is that if you can´t do your business while squatting it is time to go home! But I think that in some aspect the toilet to Chinese is like sauna to Finns, you just do your business, it is not about the partial nudity or flashing panties.
About shopping at the fake markets, if you do not plan to buy anything from a shop do not take 30 minutes of the shopkeeper’s time. They will get angry at you and an angry Chinese person can be very scary. Like if you read Daily Mail or some other paper you´ll notice that some really gruesome violent acts happen in China. I have not been under a threat of violence at any point. Some of my friends who study at Donghua tell me about the dangerous situations they have had with rickshaws and taxis. Just don’t use illegal taxis, use the ones with the meters and you should be fine.
When going out for dinner bear in mind that most of the meat dishes have not been deboned, if you are a picky eater choose your foods carefully. Chinese are also very practical about what they eat, if it is edible it most likely is a delicacy somewhere. You can find dishes made out of intestines easily, if you are a brave of heart do try them.