Do Not Flash YOUR Lights at Me!

Why? Why would someone get behind me in the slow lane and flash their lights at me? What am I supposed to do, ride on the shoulder of the road? I was even going 6 miles over the speed limit. Yes, I'm one of those idiots that will slow down when someone flashes their lights at me. So you know what they do? Pull up along side of me. I ignore them of course but I can see out of the corner of my eye that they're making gestures. I just don't get it!