This is definitely a discomforting experience. That's one of the reason I ride with someone else, most of the time. When I ride alone I try to hook up with some other riders if they are on the same road.

But if you do not have any of these options, definitely have a cell phone. You may not be able to take a pcture but you can either pretend or really call police. If he drives with an open window and hears you reporting on him, even if you are just pretending, he may just go away.

Stay safe!