I just had my first ever disagreement with a cab driver in putonghua (a.k.a. - the common language, Mandarin).
My friends and I left a dance club at 4:30am. They were all going in a different direction so I took the first taxi by myself. I told the driver that I wanted to go to Chaoyang Lu, near CCTV, and that he should turn right at the corner and drive east. He turned left and drove west. I stopped him and gave him the mingpian (namecard), complete with local map, for my destination. I reiterated that I wanted Chaoyang Lu, pointing at the name of the street, a 10 lane road, on the map and at the marker for the new CCTV building - a major landmark that anyone who has been in Beijing for more than two days usually knows about. The man made a few more turns, still going west. I stopped him again, pointed at the map, and started telling him to go left, go right, to get him driving in the correct direction. When we drover past the major construction site that is the new CCTV building I pointed it out to him. "Oh," he said, "sorry." I hadn't been speaking to him in English but the English apology seemed to be an admission of mistake on his part. He apologized again when I got out of the car.
I don't plan to go around having arguments with cab drivers. Most of them are very patient with my bad putonghua and teach me new vocabulary or point out items of interest. It just feels good to know that I can have a disagreement with a cabbie about where things are located and be right.