Last week I had a car driver try to turn right across my path - we were both on the main road, she went to turn right across my path (the driver turning left out of the side road was further away from me and did not even considered trying to pull out in front of me and the look of alarm on everyone's faces said it all - there were 4 or 5 vehicles trying to turn right and an even longer queue trying to get out of the side road), she baled and ended up half way across my lane having pulled out of the right turn back onto the main road when she realised her mistake, it left me with a little room to manoever the bike between the side of her car and the bonnet of the one waiting to get out. I simply smiled and said thank you and carried on around her because at that point I would have been blocking her had I have completely stopped. It clearly scared her what she had just done, so there was no reason to make an issue. I took it more calmly because I knew I could still have stopped if really needed - added advantage of it being uphill at that point.
Mostly though I just shake me head to myself and try not to engage them, occasionally I gester and give a 'what was that' shrug.
However, I have found that around where I am, most people are now recognising me and know that I will happily give them a smile and say thank you if they help me out, and generally they are pretty good - in fact at one crossroads where I routinely turn right, I rarely if ever have to stop despite it being a very busy junction.