To The Person Driving The Dark Grey Prius:

If it's raining, your wipers are on because it's raining, and the surrounding sky is the exact same color as your car, turn your damn lights on. It isn't that hard. And with those lights, people on the road will be able to see you. It is an amazing thing, with light comes visibility.

And while we're on the subject, maybe - just maybe - you should think about the practicality of both lighting a cigarette and talking on your cell phone while you switch lanes in your dark grey Prius without its lights on or the barest hint of a signal in the middle of a seriously torrential rain storm. Cuz speaking both as the person who nearly rear-ended you previously and also as the person you nearly sideswiped with that brilliant maneuver, I'm going to say that as far as sane and smart moves go, that wasn't one.