If someone rear-ends you, normally THEY'RE the one who's assumed to be at fault. Because they were BEHIND you, and if they didn't have time to stop, they probably weren't driving safely.
But there's a dashcam video on YouTube that proves that's not ALWAYS the case. The person with the dashcam is sitting at a stoplight, when the car in front of them starts driving forward. But then it stops, and the driver punches it in REVERSE.
(Search for "Bizarre Read-End Collision in Taiwan." It happens at 2:00.)