Monello and I were behind this nitwit the other day, all over the road, drifting, overcorrecting, drifting again. Normally I just avoid these people but for some reason I had a moment of road rage, so I honked at her several times to get her attention. This did not seem to have any effect, so I just sped up and went around her.
She was in the classic position - head down, one hand on the wheel, glancing up every few seconds....
But I'll bet if you asked her she would say, "Oh, I drive just fine when I'm texting..." because she was completely oblivious to anything going on around her.