The synchro-defecation theory holds that the defecation patterns of individuals who live together tend to become synchronized over time. The phenomenon is glaringly evident when said individuals share one bathroom.
Similar to the McClintock effect, the theory that the menstrual cycles of women who live together, such as in homes, prisons, convents, bordellos, dormitories, or barracks, tend to become synchronized over time.
Man: "I had to shit in the tub this morning 'cause my girl got to the toilet first. "
Friend: "Damn, that synchro-defecation cycle is a bitch, ain't it?"