I first heard this from my friend Maggie. We trade jokes.
Every year a pub in Dingle holds a dirty limerick contest, and every year, since the contests inception, Seamus O'Shaughnessy, the dirtiest old man in the county, wins. The prize is gentlemanly- a free pint of porter.
The contest came around again and Seamus scratched his head and arse and downed glasses of malt whiskey until inspiration struck. Snickering filthily and leering at lasses, Seamus O'Shaugnessy took his dirty limerick, yet again, into the pub the morning of the contest. After giving the barman a certain look, Seamus went home, had some soup, and recited some of his thirty or more winning dirty limericks, already savoring victory.
When he ventured back to the pub in the evening and demanded his free pint of porter the bartender shook his head.
"You didn't win this year Seamus."
"Wasn't my limerick filthy enough for you?"
"It made me sick to my stomach, Seamus, but someone wrote something even worse."
Seamus couldn't believe what he had heard. Everything went black, and there was an irritating little whine in his ears. When reason resumed her seat, he had only one question.
"Who is it what wrote a filthier limerick than me? Tell me!"
"It was Sister Mary Agnes, from the nunnery, Seamus."
Everything went black again and when Seamus returned to himself he was walking furiously toward the nunnery.
He smashed his fist into the door until someone opened it. Sister Mary Agnes greeted him shyly and inquired after his business.
"You know very well what I want. You beat me in the dirty limerick contest and I can't believe it. I need to hear the limerick that beat mine."
"Ok," said Sister Mary Agnes slowly, "but I'm too embarrassed to say the really dirty parts. So, if you don't mind, I'll simply say 'ta-ta' for those instead."
Seamus thought this ridiculous but told her to go on, out with it, let's have it then.
Sister Mary Agnes cleared her throat and recited:
"Ta-ta ta-ta ta-ta-ta
ta-ta ta-ta ta-ta
ta-ta ta-ta ta-ta-ta
and they fucked in a river of shit."