It was a marked car but it was dark and I couldn't see who it was, I only found out because I took a wrong turning and had to go back around a roundabout, was so surprised when I saw it was the 5-0!
The ones that really annoy me on the motorway are the ones that tailgate you then you pull over to let them past and they go past at 1 mph more! Makes me scream, "why the hell were you tailgating if you are not even in a rush to get past!?!?!?!?!".
That annoys me, although i then get quite annoyed and proceed to slowly up the speed and keep him alongside me for jokes lol. I had one guy pull and expression as if he thought the accelerator had stopped working before flooring it away haha