Far from the worst I've seen, just the one that's freshest in mind when I saw this thread.
Just got back yesterday from visiting family in Virginia. On the way to the airport around 5:30am, I'm driving on the interstate several car lengths behind a fuel tanker truck in the far right lane about 71mph on cruise in a 70 zone. There's another semi in the left lane. A 2nd gen Dodge diesel with body panels rusted and sagging, missing pieces, one headlight, and brake lights that activate the back up lights instead, comes flying up behind me, gets on my bumper, and starts flashing his lights at me like I should get out of his way. Again, I'm in the right lane, going the speed limit, behind another truck, and couldn't get over left if I wanted to. What is he expecting me to do, get off on the shoulder to let him be behind the tanker truck instead of me?
He proceeds to zig zag between me and the trucks to then cut the tanker truck off to take an exit about a mile further down the road from where it all started?!
Anyway, hope he was late to work.