Quite often people have triggers that cause them to need to go potty. For instance, my dog will go when we go for a walk. many times near the same location. For some people it might be just after they eat lunch, even if they don't eat lunch the same time every day.
Sometimes the bowel motivator is not obvious. Sometimes it is something that happens that your conscious mind doesn't know about. Perhaps when a bell in a small village in China is struck by a young child, you suddenly have the urge to pick up a magazine and head to the bathroom.
Maybe we all have some psychic twin somewhere, perhaps not even on this planet, it could be that it is some alien being who doesn't even have bowels; yet everytime he masturbates you have to go. Perhaps diarrhea is just your bowel-twin watching alien porn?
The amazing Randi would pay good money if we could prove this.