I've had similar where I overtook someone doing a 25-30 in a 40. Ok, only a small difference, but adds up in my eyes lol.
Anyway, as I overtake him, he decides to speed up, get up to the speed limit, then travel right up my ****. which is a bit disconcerting when he's in a big 4x4, and I'm on a motorbike, and there are speed cameras everywhere, so I can't exactly pull away much. We eventually get to the end of the road with traffic lights, where the road splits and there's a left turn lane and a right turn lane. He pulls in the left lane next to me and show off his nice collection of gestures towards me, and as soon as the lights change he accelerates hard and pulls a right, nearly knocking me off.
Needless to say, I wasn't best pleased, but the road we went on to didn't have any speed cameras and quickly went on to a dual carriage way, so I showed him my fingers and accelerated away nicely. I was just rather annoyed at him, even more so he had his entire family in the car heh.