I post and correct on a language exchange site. One day, one of my Japanese friends there received a correction from someone with the worst English I have ever seen on that site, including that of people learning English. She immediately stated that she only wanted corrections from people who were fluent in English, and asked that he not correct her entries any more.

He blew up. He claimed he WAS fluent.

After a huge row, it turned out that everyone in his village in China speaks English like that and they are convinced they are fluent. I can only assume that's because they use it with each other, and don't try to communicate with people who are natively fluent.