It's unfortunate but something that most all of us run into at one point or another. They don't know any better and with their attitude likely never will.
Never had a complaint when I had something that resembles a camera on my head, btw. Pull out your phone and ask them to repeat that, they'll probably scurry right off.
I'm pretty sure many of them know that we are allowed in the road, they are just being jerks because they think they've been inconvenienced by a second or two and feel entitled to vent their ire at us.
One of the things that I like about my helmet mounted mirror is that I can see if a car behind me has its turn signal on. Sometimes I'll pull up and over into the crosswalk to let someone behind me turn right. Whether I am on the right or in the lane varies from intersection to intersection, they all seem unique in Seattle, with their own considerations.