The ability to hold your need to go number two due to an innate fear of going in strange or public places.
It usually happens while on vacation or some other trip, most times because of the fear associated with dirty public restrooms or having to go in the midst of those with you. The constipation can sometimes last for days, a feat seemingly impossible on normal days or at home.
When Noah and I took a trip to Disney World...I had the worst case of vacation constipation. I didn't take a crap for 4 days. I was afraid to use those dirty, puke-filled bathrooms, but man it felt good when I got home!