Constipation

A nun walked into a bottle shop and asked the shopkeeper for the biggest bottle of cheap rum they had. When the shopkeeper handed it over, she whispered "It's for Mother Superior's constipation".

A few hours later, the shopkeeper closed up and when he went to the car park, and saw the nun staggering around, singing loudly and clutching the empty bottle.

"My God, Sister!" the shopkeeper said. "I thought you said that rum was for Mother Superior's constipation!"

"It is" the nun slurred drunkenly.

Spoiler:

"If this doesn't give her the sh*ts, nothing will!"