I had a pedal that had been cross threaded into the crank arm once. About 2 miles from home it had worked it's way loose, tearing up the threads leaving no way to put the pedal back in. And when I stopped to check on that I found a tack nail sticking out of my tire.
It was a used bike I had just bought cheap. I was just giving it an initial ride to see what it needed. The ride started off great so I went further than I planned on. I didn't have any of my repair stuff packed onto it yet (tube, tools, etc)....pro tip...don't do that.
So there was no fixing it and nursing it home. I just had to walk.
$40 worth of parts and repairs later and the bike is running good as new though!