I think the biggest comprehension problem, it that many Chinese people are not used to hearing people using the wrong (or mangled) tones. This just confuses. Especially true if people use the wrong sentence order.

Many a time I have called my mother-in-law '(v) scold' or a 'horse'.

I have noticed that sometimes Chinese people just don't expect that Laowai will be speaking in Chinese to them and this makes it imposible for them to understand.

@Yuantongsi

I think you are right. An American friend speaks well enough to be a manager in a Chinese software company, the only non-Chinese employee. He says sometimes the Chinese don't even realize they are in a conversation, with this big laowai guy, in Chinese. Even to the point of asking, one of the pre-programmed questions. after a few minutes of conversation in Chinese, do you speak Chinese?

A stereotype is attached to a white face; we are not intelligent, we have money, we don't speak Chinese, and we are capable of getting angry easily. In short, at best a laowai is a pain to deal with and at worse will behave irrationally. Of course, Chinese are never that way.