Draw your own collisions

Was this in France? I had bad experiences there last summer, due to my ignorance of the 'priorite a droite' rule. On one occasion I was bombing down a hill when a car pulled up to the entrance of a small road to my left, saw me, and proceeded to pull straight into my path. Much fishtailing and swearing ensued, though luckily I managed to go around him without clipping his bumper. Another time on a roundabout I had a similar encounter to yours, with a 18 wheel HGV... I still can't understand why it's like that, it seems to negate the point of roundabouts entirely.

It's not like that, if I understand your story right, the 18 wheel HGV was in the wrong there. There is no "Priorite a droite" on roundabouts in France: as far as I know they work on the same principle as in UK. You owe right of way to whoever was engaged on the roundabout before you. It is actually forbidden to stop when you are in a roundabout, so once your are there, you are not expected to give right of way to people coming onto the roundabout from an adjacent road.

Now, outside roundabout, "priorite a droite" is a bit of a bitch sometimes. I don't like the way that depending on the road you are on, they may or may not apply... Can be confusing sometimes, however the rule that define how they work is pretty clear and makes sense, you just have to know it (which is not easy if you did not pass your theory in France...)