So not a mechanical problem, but how about a weather related one? I was out for a ride, approx 40k from home when the skies just open and the rain came like it hadn't rained for days. After getting thorough drenched and seeing no end in sight, I decided to call it. There was no way I could bike home in the downpour, not to mention the fact I was FREEZING cold.
I opted to drop by the apt. of an ex-GF. Luckily we ended on good terms, so I decided to beg her for a ride home. As luck would have it though, she was NOT home. With my tail between my legs, I shlepped to the bus stop an took two buses to get home, leaving a nice wet puddle on all of the seats I sat in. Needless to say I was a shivering mess when I finally arrived home. At least it was still raining, and continued to rain for hours after, so I felt kind of vindicated.