I know it's an old one, but I like it. 

Rob kissed his wife, crawled into bed and fell asleep. All of a 
sudden, he woke up to find an elderly man dressed in a white robe standing at the foot of his bed. 

"What the hell are you doing in my bedroom?... and who are you?" he asked. 

"This is not your bedroom," the man replied, "I am St. Peter, and you are in heaven." 

"WHAT! Are you saying I'm dead? I don't want to die! I'm too 
young," said Rob. "I want you to send me back immediately." 

"It's not that easy", said St.Peter. "You can only return as a 
dog or a hen. The choice is yours." 

Rob thought about it for a while, and figured that being a dog is too tiring, but a hen probably has a nice and relaxed life. 

"I want to return as a hen." 

And in the next second, he found himself in a chicken run, really nicely feathered. But now he felt like his rear end was gonna blow. Then along came another hen. 

"Hey, you must be the new hen St. Peter told me about," she said. "How do you like being a hen?" 

"Well, OK I guess, but it feels like my ass is about to explode." 

"Oh that!" said the other hen. "That's only the ovulation going 
on. You need to lay an egg." 

"How do I do that?" Rob asked. 

"Cluck twice, and then push all you can." 

Rob clucked twice and pushed more than he was good for, and then 'plop' an egg was on the ground. 

"Wow" Rob said, "That felt really good!" 

So he clucked again and squeezed. And you better believe that 
there was another egg on the ground. 

The third time he clucked, he heard his wife shout: 

"Rob, for Christ's sake! Wake up! You're shittin' all over the 
bed!"