Hardcore bikers are a strange lot, they get almost militant about what they do. The driver is obviously an ass for littering, but she was just as guilty for her knee-jerk reaction to the whole thing.
I almost got into it with a biker one day where I live, riding in the middle of the road and holding up at least 20 cars. A few people shouted at him to move to the side (including myself), there was a bike lane for him. We got around him, stopped at a light and he caught up and decided to give me a piece of his mind. He spit on my car, and then pulled out his bike pump and started waving it at me. I felt threatened, got out of my car and he then realized that at 5'9" and 150 with a biker body, he was not going to do anything but take a beating from his own pump by me, at 6'4" 240.
I am thankful he pedalled away, I would have gone to jail for beating him senseless and it just isn't worth it. This was when I was about 25, younger and dumber.
I have mellowed since, but some of these bikers just go way too far to prove they belong on the road with cars.