Talking in "whispers"
Don't speak in Chinese about us when we are within earshot, this one I feel is downright rude. Try not to guess our nationality either, not all black people are from Africa (and p.s. Africa is not a country, it's a continent) and not all white people are from America. There are a multitude of different countries, nationalities and ethnicities out there, it's better instead to simply ask them.
Generalizing
This is one of my biggest gripes. Whenever I am talking to aChinese person and they state "all you westerners drink milk, yeah?" or "you are all very rich" or any other generalizing, sweeping statement, I get annoyed quickly. Chinese people are proud of their country, their uniqueness as they should be, but don't forget that so are we and we don't like to be lumped together as one country called "The West" we have many different and proud cultures and countries, just as many if not more than China and we don't like to be generalized into one condescending mass of westerness. It's frustrating to say the least and it puts me off talking to the person.
Picture taking
Do not, under any circumstances, try to take a picture sneakily without the person knowing, it's not a zoo and we are not animals. I have had people on buses sitting next to me try to take a picture of me and him sitting next to each other so they can then show off to their friends that they know a foreigner. It is extremely rude and even within Chinese culture you would not appreciate someone doing it to you. If You want to take a picture...simply ask. If you ask, most foreigners will be happy, but if you try to sneak a picture, you will make many of us very angry.