OK, I'll add some of my own.
12 years old, pedaling away from the house looking down at my feet and wondering "Should I go back and put on my other shoes - they look cooler than these ones". Straight into the back of a neighbor's parked car. It bent my forks way back and as the repair cost was an astronomical sum of GBP 4.50, my parents made me save for it out of my (50p per week) pocket money. It was one of those rare events, a beautiful British summer and my friends were out on their bikes every day of the school holidays. Not me. Finally had the right amount of money just as school started up again.
Fast forward a few years, a friend and I rode Lands End to John O' Groats (far southwest of England to the far northeast of Scotland), youth-hosteling it along the way. Day 1 required us to spend most of the day on the train from the north country down to Penzance near the southwest tip. From there we had a quick 10 mile ride to Lands End for the photo then back to Penzance before starting the trip proper the next day. 20 miles? No bother, we'll just knock that out after dinner.
Except we forgot that it gets dark earlier in the south than in the north where we lived and by the time we turned around, the last of the daylight had gone. And neither of us had lights on our bikes. 10 miles doesn't seem all that far on a map but these were twisting, narrow, shoulderless and disturbingly busy country roads. I was dressed in black on a black bike. My friend in navy blue. One driver made a point of stopping to yell at us and I think it was because we'd really frightened him. We both had a brandy in the pub when we finally made it back to the hostel.
OK, one more. A group of friends and I decided to race the last 5 miles back to town to try and catch the chip shop before it closed. Astonishingly, I left them all in the dust. Man, I was cruising. Way out in the lead with my head down I crossed an intersection and hit the central median straight on. I remember the feeling of frustration that my brakes didn't appear to work. My friend Pete, in second place explained this would have been because my wheels were some eighteen inches off the ground. No bones broken but the resulting abrasions meant I couldn't ride my bike for weeks. Yes, alcohol may have been a factor in this one.
These were all many years ago but I can't honestly say that age has brought much of this wisdom I keep hearing about.