1. Don't stick your chopsticks upright in your rice.
2. If you're offered a gift, refuse to take it a couple of times.
3. Same thing with compliments.
4. The Chinese population is gradually declining.
5. Eating dog is becoming increasingly unpopular.
6. Breathing in Beijing air is not as bad as you might think.
7. The one-child policy does not apply to everyone.
8. China is not technically a communist country.
9. Ask a Chinese person how to access blocked websites.
10. Chinese people don't speak "Chinese."
11. You won't necessarily be the tallest person in the room.
12. Each Chinese character not an individual word.
13. No one in space will be able to see you on the Great Wall.
14. There is a good chance you will have to use a squat toilet at some point. Don't be afraid.
It's actually more sanitary than using a regular toilet. Just remember to BYTP (bring your own toilet paper).
15. Explore beyond Beijing and Shanghai.
Though everyone should visit both places at least once, China has so much more to offer than most people tend to talk about. The south of China is great for spicy food and cities like Suzhou (the "Venice" of China) and Hangzhou (known for the West Lake) in Eastern China are a little more off the beaten path. Make sure you hit some real natural beauties though, like Karakul Lake in Xinjiang in Huang Shan in An Hui.
16. The Chinese food you're used to eating in the USA/Europe is probably not real Chinese food.
Sweet and sour pork, egg rolls, beef and broccoli... Yeah, Chinese people don't eat that. Instead, you'll find more cooked vegetables and simple meat dishes. Different, but delicious.