I just have this daft tendency to put my arm out when I'm falling over! Resulted in fracture and dislocation of my elbow that time. I managed to fracture the head of my right humerus all on my own once falling off in slippery, foggy conditions.
I was cycling on London Bridge and the pedestrian ran across the road to catch a bus, not looking properly although I saw her and tried to take evasive action. She ran into my bike so I fell and caused serious damage to my arm. 100% her fault. If you read the Highway Code as to how you should cross the road it's quite interesting and she broke most of the 'rules' (I know they're not rules just can't remember what they are).
It was settled out of court given that she was unlikely to be able to pay the probable award in which case we'd then end up relying on my insurance to pay me! From the names on the cheque it looked like she'd borrowed the money from her sister. I have no qualms about that. I have to live with a permanently damaged arm.