I see grey hair above the driver's headrest on the car in front and immediately drop back. Saw one old boy blindly follow someone onto a roundabout when if he'd looked for a second he would have seen a car he should have yielded to. Was a couple of cars behind (presumably) a doddery old person, pootling along at 40 in a 60 limit on a clear dry day, and then proceeded to completely ignore a 'give way to oncoming vehicles' sign and trundle over a narrow bridge. Was stuck behind another one on the way home from work the other night, going at no more than 25 in a residential area, but still slowing to a crawl for every speed bump.
Micras also seem to be owned solely by the incompetent. Had one pull out to overtake a cyclist with traffic (ME!) coming the other way.
Idiots that pull out and cause me to slow or brake sharply - one pulling across my lane to go the other way on a 30 road, not so bad, but the one that pulled out in front of me on a 60 road, oh that was stupid. However he did apologise and was French so it was forgiveable.
Buses are usually quite courteous, but I was coming the other way towards the aforementioned narrow bridge, and I know how people really object to giving way, so I took up quite an aggressive position to assert that I wanted to cross. This bus who, if the driver was able to plan past the front of his vehicle, would have seen me waiting decided to come across anyway, but then couldn't get round the tight corner on my side, and just sat there looking at me expecting me to move!
I think drivers who haven't read the highway code since they passed, or have lost the ability to drive since passing (or not in the case of some seniors). But I think it has taught (and is still teaching me) to anticipate others questionable driving better -
Coming up to a roundabout on a 2 lane dual carriageway in the nearside lane, a car matches my speed in the offside maybe half a car length ahead of me. I drop back slightly so there's enough space for him to fit in if he wants/needs to, and sure enough he indicates and moves across to my lane and then the left turn lane on my nearside.