After years of worrying about it, I finally got clobbered one night riding home from work in Aberdeen a few years ago. Narrow street, dark, cars parked all along both sides, car coming the other way which only just fits. (I had three front lights - including one on my helmet and one very bright one).

Somebody had been waiting for that car to pass and then opened their door.. all over in a flash. It was a slight uphill but I was pedalling firmly and collected the corner of the door against my chest. The bruise lasted quite awhile. A couple of inches higher and I think I would have broken a collar bone. The driver got quite a shock too..