On a somewhat related note, I was once driving down a highway, and a guy came up behind me at a frightening speed swerving around all the traffic with his emergency blinkers on. I couldn't help but think that the emergency blinkers look like both turn signals at once, so maybe they just thought if they hit the emergency blinker button, they can switch lanes however they want to.

By the way, if somebody does come up and drive like that, with or without the emergency blinkers, just let them drive past, man. If you block them, you never know, you might be blocking a person with a real emergency. I know it might feel irritating, but with your limited information, the best thing for everybody is if that person gets past you. There have been cases in the past of medical emergencies where the driver was intentionally blocked from passing and a person in their car died.