She was in Japan to visit some friends. Although she speaks English and Mandarin fluently, she doesn't know any Japanese, so her friends taught her how to say "Sorry, I don't speak Japanese." She managed to say this sentence quite well despite learning it purely phonetically.
One day they were walking down the street as a group, and a gentleman approached and asked her for directions. She responded with the only sentence she knew: "Sorry, I don't speak Japanese."
The gentleman was offended by this response and began scolding her for her rudeness. "Look, if you don't want to talk to me, just say so. Don't pretend like you don't speak Japanese." Since he was scolding her in Japanese, all she could do was stand there bewildered while this guy yelled at her.
Fortunately, her friends intervened and explained to the gentleman, "No really, she doesn't speak any Japanese. We just taught her that one sentence."
The lesson I took from this story was that when you don't speak a language, it's important to sound like you don't speak the language. In a way, it's a good thing that my German is a little bit off. That way, the person I'm talking with knows that my German is not all that great.
Examples: During a trip to Germany, I discovered that when I asked a simple question, people would answer in rapid-fire German, overflowing my internal parsing buffer. During my trip to Sweden, I applied the lesson from this article, and found that people switched to simpler Swedish and spoke more slowly. As a result, I had little difficulty understanding what people were saying to me. (Of course, it didn't help me understand what they were saying to each other.)