Nun

Arthur was sitting outside his local pub one day, enjoying a quiet pint and generally feeling good about himself, when a nun suddenly appears at his table and starts decrying the evils of drink.

"You should be ashamed of yourself young man! Drinking is a Sin! Alcohol is the blood of the devil!"

Now Arthur gets pretty annoyed about this, and goes on the offensive. "How do you know, Sister? Have you ever had a drink yourself? How can you be sure that what you are saying is right?"

"Don't be ridiculous, of course I have never taken alcohol myself"

"Then let me buy you a drink. if you still believe afterwards that it is evil I will give up drink for life"

"How could I, a Nun, sit outside this public house drinking?"

"I'll get the barman to put it in a teacup for you, them no one will know"

The Nun reluctantly agrees, so Arthur goes inside to the bar. "Another pint for me, and a triple vodka on the rocks", then he lowers his voice and says to the barman "... and could you put the vodka in a teacup?"

"Oh no! It's not that drunken lush Nun again is it?"