Last night, I was driving with my girlfriend in SF, and we made a left turn onto the leftmost lane of a 3 lane street (19th Ave). Someone from the other side made a right turn onto the same street, but moved from the rightmost lane they were supposed to go in to the leftmost lane. (picture=1000 words: http://i.imgur.com/1cyok.jpg . We were the red arrow, they were the blue/gray arrow)
We came within centimeters of a collision for something really dumb because this guy wasn't paying attention/was a poor driver/etc.