We had one driver in front of us on a very curvy road some time back. The driver (a female) was crossing the drunk bumps into the oncoming lanes, and then cross into our lane. I thought she was DUI, and decided to stay behind her. We caught up with here at a traffic light, and she was texting. After the light, she got off the texting and into the right lane. Drove normally after that.
And like Mr Magoo, she probably had no clue of the danger she narrowly escaped.