After 6 days in Brazil, where I tried very hard not to drink the water, the nightmare started on an international flight from Rio to Dulles and ended in all of its glory standing in line at immigration. Fortunately I had an inkling that things were not quite right before the flight so I put a backup pair in my briefcase.
Everyone's worse international travel nightmare began for me about 3-4 hours into my flight but, luckily, I was able to make it to the lavatory, the same happened a few hours later but I again I was lucky as there was no line.
After landing I made a tactical error thinking I could get through immigration before the next wave, but this time I was not so lucky. As I was standing in line I realized that things were no longer under my control. I handed my passport to the immigration officer, trying to maintain my composure with what I was sure was a disaster to my rear. After getting through immigration I rushed to the nearest bathroom and my worst fears were confirmed. Fortunately most of the detritus passed on the plane and I had my backup pair so I could at least make myself presentable but a perfectly good pair of kakis were ruined.