That's an easy one. I saw an old, steel tandem in someone's front yard when I was eighteen. I bought it for $20.00. It had one cheap brake with a plastic handle that was more like a device for slowing down than an actual brake. My sister and I would take it out for rides when we were feeling adventurous.
The best ride ever on the steel death trap: Going down the local river trail on a nice, sunny day. I'm in front and she's in the back. She can't really see much, but I'm much better with the steering and a better judge of distance for using the "brake" so we'd learned we stood a much better chance of survival with me in front.
Anyway, there we were blissfully peddling our way along the river. She starts yelling, "Water! Water! Water!" I look ahead to where the trail goes under a bridge and sure enough, the trail's flooded out. Now, a clever person would put down their feet to balance the bike as it hit the water. Not my sister. I suddenly feel her feet kicking and pressing into my back. She's got her legs up on the top tube to keep her feet from getting wet!
Well, the "brake" kept us from hitting the water full-blast, but we didn't stop until we were half-way under the bridge and I'm up to my thighs in water balancing her and the bike with the water just an inch below the top tube and the current pulling strong. I work my way off the bike, keeping it balanced the whole time, and trudge my way back to the trail, pushing the bike (with her still on it and her feet on my seat) backwards out of the water.
I held on to that bike all through college, single life and seven years of marriage. It now resides in the local landfill but it will forever live on in my memory. And nightmares.