All those highly-processed snacks in supermarkets like weird flavoured nuts, dried meat, chips etc. They contain a tonne of artificial flavorings, colorings, sweeteners and preservatives, many of which I'm sure are banned in the West. And not to mention high MSG and sodium levels.

I agree with Redaria, I try avoiding eating too many dried fruits and things like that because of the preservatives. However, despite all the milk scandals, I drink milk every day, so I guess I'm not doing myself any favors.

I avoid eating candy of all kinds. I've been to the dentist and there isn't anything wrong with me. But I wouldn't let myself get addicted to all those sweets because you are what you eat and I wouldn't want to turn into a sweet tooth. Nuts are good too! Avoid too much excess sugar in foods! 

I completely avoid fresh-water fish in China.  Most places you can't drink the water due to high levels of heavy metals present and this is often the same water where the fish are taken from.  These toxins are also in the fish.  Besides the fact that all freshwater fish I have tried here either has a metallic taste, or even more often, they taste like mud, so I just don't bother.

I also avoid local cheese and chocolate, simply because they aren't good.  At all.  The "cheese" is well, uh, exactly, but not completely, entirely unlike cheese.  "Chocolate" here seems to basically be hard brown butter, but without the flavor.

mc donald's

street food cooked in oil. (in nanchang stay away from all street food)

Chicken feet, 'cause if I ate them it would absolutely kill me.