This could be taken as a challenge! I'm sure many potential commenters out there could put forward their own candidates.
But, in honour of the imminent St Patrick's Day, here is one of my favourites.....
An Irishman is marooned on a tiny desert island.
As he walks disconsolately around and around his tropical prison, he happens on a small, exotically-coloured bottle half-buried in the sand.
The Irishman picks it up and examines it, removes the cork - and, YES, out puffs a Genie!
"Thank you for releasing me, Paddy," says the Genie, with something less than the deference that is customary with his kind. "In accordance with tradition, I must now grant you three magical wishes. You may have whatever your heart desires."
"What - anything?" boggles the Irishman.
"Yes, anything," repeats the Genie patiently.
"Well," says the Irishman (who is desperately parched, after spending a couple of days on the island without attempting to find water),"I could murder a Guinness!"
"Your wish be granted," says the Genie. And out of thin air there appears in the Irishman's hand a perfectly-poured, ice-cold pint of the black stuff.
The Irishman eagerly glugs it down, and smacks his lips in appreciation.
He is about to toss the empty glass into the ocean.... when he notices that it is suddenly full again with another creamy-headed, velvety smooth pint of the black beer.
"Saints preserve us!" he cries. "What's going on here?"
"It is a magical beer glass," explains the Genie. "It will always be full again one second after you empty it."
"Ah, man, yer havin' me on!"
"No, really, the glass will always fill itself with Guinness again."
"What - really?"
"Sure, that's a marvellous thing! I never seen the like."
"Well, that's what we call 'magic'," says the Genie modestly. "Now, what would you like for your other two wishes?"
"I'll have two more of these!" shouts the Irishman delightedly.