I'm a fast driver, so if someone is coming up behind me and flashing their lights like they want to get by me or they're riding my ass... I get out of the way. When I'm in a crazy hurry, I do the same thing to people and usually they get out of my way. If you're in the left lane and someone obviously wants to get by you then just let them. It's the safest thing to do and there is 0 reason why you shouldn't try your best to get out of their way. What will eventually happen is they will get frustrated and try to go around you on the right and who knows what risks they are willing to take... just let it go.
The only time I flashed my lights at someone and they didn't move over was in southern Jersey. I was driving my father's 2001 Impala down to MD since they had just moved. I went around them on the right side, and this van full of thugs sped up next to me rolling down the window and motioning for me to pull over, swerving into my lane and stuff. This went on for a few minutes and they weren't paying attention to the road in front of them. Finally, they hit what looked like a muffler hanging out on the shoulder and blew out their left side tires. I didn't slow down to see how bad it was... I just laughed and kept going.