In the three accidents where I was driving:
A ford explorer in front of me on a 2-lane road going about 45mph turned into an apartment complex, then used their drive to do a big sweeping U turn back across my lane, and through a stop sign (for the driveway people turning onto the main road). I was 17 years old but I don't fault myself for not driving more defensively. The guy just turned into the apartments, when he swooped back out I swerved but it was all very quick. That's not something you're prepared to defend for until you've seen it happen, frankly.
The next one was very minor, but we had two left-hand turn lanes and we were approaching a traffic light. I was in the right-hand lane, with no cars directly in front of me. I had a red car to my left, and a black car in front of him. The light turned yellow, and the black car was going to stop. The red car swerved quickly into my lane to go around the black car, and he clipped the front of my car. It knocked off a light cover, but otherwise no real damage. He ran the light and did not stop. There was no time to react, he literally yanked his wheel over, and I could not swerve right anyway, as there were vehicles there.
On the motorcycle, I was driving on a two-lane road behind a large vehicle, I think it was an SUV. Someone was waiting to turn left in the opposite lane (so they wanted to turn across our lane). There were many cars behind me as well. The person didn't see me and turned after the SUV passed. They stopped halfway through the turn, by which time I had already put down the bike while slamming on the brakes. The bike hit the car and totaled, and I slid down my lane with virtually no injuries. I was fairly well equipped so I just had a couple of very minor scrapes. She had no insurance. This accident was most avoidable in theory. Perhaps I could have positioned myself better, and she might have seen me. But probably not. I could not have swerved around her, though, unless I anticipated her stopping halfway. If she didn't stop halfway, and I swerved right, I would have gone through her passenger window. If I swerved left, it was a head-on collision.
During all of the other accidents, I was not the driver.