I don't know if everyone else here will back me up (I hope they'll join the discussion, it's nice to have a chat about this) but in that situation you can get an instinct of when people have or haven't seen you.
It's like when you are waiting at a junction and you see a car coming along with it's left indicator on, a new road-user may pull out, a more experienced one would think that they're going too fast and wait for the car to pass you. The same applies to this, the body language of the driver, the type of car, everything gives you an idea of what will happen.
I know whenever I see a car waiting to pull out my thumb is on the horn, I'm rolling off the gas and I'm waiting to see the wheels move, if they do you hold the horn down for as long as it takes for them to stop. Of course, it depends on how close you are, if you're a few meters away you should really just stop/go round them into the oncoming lane if it's clear... What I'm trying to say is that with enough planning and experience you can overcome the majority of things that are thrown at you.
Car drivers that are trying to mess with you by getting too close? Pull over and wave them by! There is honestly a good way to deal stuff on a bike
I wouldn't do it on a harley, I'm not a cruiser guy, I'd do it on some sort of adventure bike, maybe even my little BMW. I was silly to ride it unrestricted, I'm going to miss the full-fat of 45bhp! :P