Bob and Christian
Bob and Christian were prawns. Theirs was a tenuous life. Being near the bottom of the food chain, almost everyone else in the ocean was a predator. They spent most of their lives, and a lot of nervous energy, watching their backs and bolting for the nearest hide when a predator came too near.
One day, while swimming about their business, bitching and moaning about their station in life, Bob said, “I’m sick of running from everyone... I wanna be a shark! Then everyone would run from me!”
As it happened, this statement was made within earshot of the Magic Cod…
No sooner had the words (or prawn equivalents) been uttered than, POOF! Bob was a shark.
Christian took one startled look at his best mate’s new dental equipment, and bolted.
The emboldened Bob was somewhat surprised, but pleased with his new status at the top of the food chain. Fearing no-one (except possibly the Giant Squid), he roamed the ocean, devouring whom and what he pleased.
However, (there’s always a ‘however’!) he found his new life lonely, so went in search of the great Magic Cod.
Eventually he found the M.C. and asked, “Could you please return me to my old self? I’m so lonely, and I miss my best mate, Christian.”
“Well,” said the Magic Cod, “seeing as it’s because of friendship, I will relent.”
POOF! He was once again a prawn.
Anxious to show off his restored prawnhood, he immediately scuttled back to his old home, but found no-one he knew. So he asked a passing shrimp (he was an American tourist) where everyone, especially Christian, had gone.
“Well, there was this amazing story,” said the shrimp, “Christian claims his best mate, Bob, was turned into a shark, and he’s locked himself in his house. He says he’s not coming out until that shark is dead.”
This dismayed Bob, who immediately went to show Christian he was once again his old self.
Bob knocked on Christian’s door and called out to him, “Christian, it’s Bob, I’m back!”
“Go away, Bob.” said Christian, “I’m afraid you’ll eat me.”
“Please, Christian, let me in, it’s OK!”
“NO!” shouted Christian, “you’ll eat me!”
“It’s alright,” replied Bob, “I’ve found Cod, I’m a prawn again, Christian!”
(Don’t geddit? Read the punch-line aloud.) 
Oh wrong one sorry bout that. 
