"Drunk Nuns" joke

These two nuns walk into a liquor store one evening just before closing time.
They select a cheap bottle of brandy from the shelf and attempt to check out when the clerk begins hesitating.
"Excuse me sisters", he says shyly, "but I don't normally sell alcoholic beverages to nuns."
It's perfectly okay they reassured the clerk," this is strictly for medicinal purposes."
"Very well" said the clerk, "that will be $6.50"
The nuns thanked him and were on their way.
About twenty minutes later, as the clerk is locking the front door, he notices the two nuns staggering down the street, obviously drunk.
He approaches the two and in a very stern voice says "I am ashamed of you two!
You lied to me and told me that the brandy I sold you was for medicinal purposes only, and just look at you now!"
To this the nuns replied "Don't feel bad kind sir, we did not lie to you .
You see the Mother superior has been constipated lately and when she sees us, she is going to SHIT!"