This question was inspired by Flying Merkel's comment of "Buy a crappy old pile. Ride it. Every thing else will be an up." in the "12 bikes in two years. am i being picky?" thread.
Most of us have had or ridden a crappy old pile or two. Tell us about them.
I have two. Both of which I shared with my brother.
The first was a three speed, maybe a Raliegh, but the "English Racer" style. My Dad bought it used. When I took it on the test ride, everything worked okay, but I got a creepy feeling about it. My brother and I were to share it. From my experience, it was like a fractious colt that loved nothing more than to buck off its rider, and it seemed prone to handling mishaps. I went off to college, and my brother, faced with riding it, rode it into a bad neighborhood and "forgot" to lock it and walked home.
That led to the next bike, a Montgomery Ward 10 speed. My Dad bought it for my brother after the 3 speed. It had fenders and tried to look like the 3 speed. He didn't like it much either, but brought it along when he moved from Dad's to Mom's. It was on the balcony of his apartment 8 years later, (his Peugeot got the riding) when I moved in with him to go back to school. He got a good job elsewhere and moved, leaving the MW behind.
Then, a month before I graduated, I was caught in a crunch, all my bikes needed work and I was running on financial vapors. I remembered the MW. I tried inflating the tires and they held air. Then I applied WD-40 to the drive train and it sprang back to life. Hoo Haa! It was uncomfortable, but it worked like a champ; for two weeks. When suddenly, while riding back from class the bike felt bizarrely soft. Then it felt like it was changing dimensions. I pulled over and the downtube had separated from the bottom bracket. Happily, I was able to pull the frame back together with turnbuckles and baling wire, and made it through to graduation. The frame died 3 days later on the way to work. I stripped all the components off and threw the bike in the dumpster. The rear derailleur got reused and is still in service.