For the right hook (or the situation the OP described), my vote is "plain stupid," or rather more like "don't care because we're vulnerable and they're not."

They just passed us. So they know how fast we're going. If they had to speed up to 35 mph to get around us, it doesn't take a rocket scientist to figure out that if they then take the right-hand turn at 10 mph, or jam on their brakes to a complete stop, they're going to cut us off.