Then there's the SUV (it always seems to be a SUV) that made a last-minute decision that the lane I was in was the better lane for a set of lights and so changed lane right in front of me just as we reached the queueing traffic. I suppose it is actually the better lane if you're following the main road, as the other one just gets stuck in a queue on the roundabout itself. This is one of those things where local knowledge (or forward planning using Street View) helps as then you know well in advance where to be - for example, after a few trips to Horsham and back I now know exactly which lane to be in the M27 to sail through all the junctions around Portsmouth without getting caught up with filter lanes (inconvenient) or the M275 merger (downright evil).
Oh, and as proof that it's not just some drivers but all of 'em that're up to craziness, there's me trying to enter a roundabout from almost-stationary, in 2nd gear. While going uphill. Yeah, not quite enough torque for that to work well in this car... that said, I did make it without stalling (which would have been most unpleasant on the middle of a roundabout).