In my teens, I sometimes used to hold back the urge for about 2 days. But in a way I'm the opposite of most sufferers, because I actually prefer to evacuate somewhere like a public toilet, with long rows of cubicles. I dread going for a Number 2 at home, in case it won't flush away for ages; if you're in somewhere like a service station, or department store, if it turns out to be unflushable you can just walk away and forget about it.