This happened a few years back while I was a weekend trip with my wife to Savannah.
Savannah is a historic area. It is made up of several historical squares with a nice downtown area. There is also several ghost tours set up, being that Savannah is one of the most haunted places in America (if you believe that sort of thing). My wife wanted to take a ghost tour, and you had to reserve a spot in advance. Also, unlike most of the tours, this one was a walking tour as opposed to the trolley or other vehicle tours.
We had the day set perfectly. We toured some downtown sites, ate lunch out and walked back to the hotel to take a nap. After we woke up we had a nice dinner before the ghost tour. It started at 9:30pm, and we were kinda early, so we puttered around a bit until it was time. We treated ourselves to some ice cream to pass the time.
When it was time for the tour, I was feeling pretty full from dinner and ice cream but I figured the walk would help me digest my food easier. As the tour progressed, we moved out of the more commercial area and into more residential areas. Also as we progressed, my fullness turned into a more bloated feeling. Slowly down to the back of the group, I started letting out gas a bit at a time to try to ease myself. But the bloatedness wasn't going away. I didn't want to stop the tour, but I wasn't sure how far we would move away from public bathrooms and how sure it would continue. Eventually the gas was becoming less and less, and the pressure still built up. Finally, I tuned to my wife and whispered "I need to take a crap. Like, right now." We had walked about 4-5 blocks at that point and I needed to get back to somewhere that I familiar with. She said she'd stick with the group and tell the tour guide of my absence when he finished with his spiel. I turned about face and started heading back into the direction from which we came.
I was really only recognized one street and I knew it had a bunch of restaurants and shops on it so that was the street I headed down on. I walked a brisk pace, because at that point I was not chancing a run. A few times I needed to stop because my stomach would start gurgling and it took all my strength to clench my butt hole closed. I was about 2-3 block from the nearest shop and I had a feeling that they were closed for the night. I was far enough away from my hotel that I knew I wasn't going to make it that far so I tried my best to see if I could find someplace that was open AND had a public bathroom.
2 blocks to go, I almost doubled over in pain. I was prairie dogging it now and needed to make a decision fast. Either I could try running and risk the chance of shitting myself, walking and risk the chance of shitting myself, or drop my pants and crap on the sidewalk. I kept walking but knew the next time it started pushing, I was going to have a little brown baby.
With some luck, the next time it hit me I was three steps away from a local car dealership. It was dark, and I could duck between a couple of cars so no one would see me from the road. I rushed between the wall and a big SUV, pulled my pants down and squatted like an Olympic gold winner. What came out of my bowels was the size of a 3 year olds arm and probably smelled just as bad. As I was quite relieved, I took a few moments to catch my breath and think of the next step of the plan. First, there was the issue of what if they have security cameras? It was dark enough and I was willing to risk that they wouldn't go prosecute me for taking a public shit. Second, I started feeling bad to whoever had to come across that in the morning and eventually clean it up. The thought soon fleeted from my mind, noting a car dealership probably had some car wash equipment they could might be able to clear the offending turd away with. Lastly, I knew this wasn't over and I still had to make it back to the hotel.
I was lucky enough that my continued journey didn't have any perils and I was able to make it safely (minus a pair of boxers that were shit stained from the experience).