There are many versions of this, some better or worse.
Once upon a time, there was a man who decided he wanted to get away for a bit. So his filled up his truck with gas and filled his motorcycle with gas and put it on the back of truck. So he gets in the truck and he drives and he drives and he drives and he drives and he drives and he drives and he drives and he drives and he drives and he drives and he drives and he drives and he drives and he drives and he drives and he drives and he drives and he drives and he drives and he drives until he runs out of gas.
Then he takes the motorcycle off the motorcycle off the back of the truck and he rides and he rides and he rides and he rides and he rides and he rides and he rides and he rides and he rides and he rides and he rides and he rides and he rides and he rides and he rides and he rides and he rides and he rides and he rides and he rides and he rides until the motorcycle runs out of gas.
So he gets off and he walks and he walks and he walks and he walks and he walks and he walks and he walks and he walks and he walks and he walks and he walks and he walks and he walks and he walks and he walks and he walks and he walks and he walks and he walks and he walks until he can't walk anymore. He reaches a hotel and walks in to ask if he can have a room.
"Sure," says the manager, "but I have to tell you one thing." So they go into the living room where there's a table. He takes the candlesticks off the table, the chairs away from the table, the table off the rug, and the rug off the floor. There's a trapdoor there, which opens to reveal a long flight of steps.
So they climb and they climb and they climb and they climb and they climb and they climb and they climb and they climb until they're down the stairs. They're now in a long tunnel, so they walk and they walk and they walk and they walk and they walk and they walk and they walk and they walk and they walk until they reach a wooden door. He picks the key up off the floor, unlocks the door, opens the door, goes through the door, locks the door, and puts the key back on the floor.
And then they walk and they walk and they walk and they walk and they walk and they walk and they walk and they walk and they walk until they reach a metal door. He picks the key up off the floor, unlocks the door, opens the door, goes through the door, locks the door, and puts the key back on the floor. There are two green hills, so they walk and they walk and they walk and they walk and they walk and they walk and they walk over the two green hills. They finally reach a clearing with a table. On the table is a cage, and in the cage is a purple gorilla.
"Whatever you do," the manager says, "don't touch the purple gorilla." And so they turn around and they walk and they walk and they walk and they walk and they walk and they walk over the two green hills. Then they reach the metal door. And do everything backwards. (Note: Keep telling it here to annoy people. I just don't feel like typing it.) So, the man is lying in his room later and thinks, "You know, I wonder why I'm not allowed to touch the purple gorilla."
So he goes into the living room. He takes the candlesticks off the table, the chairs away from the table, the table off the rug, and the rug off the floor. And he climbs and he climbs and he climbs and he climbs and he climbs and he climbs and he climbs and he climbs down the stairs and he walks and he walks and he walks and he walks and he walks and he walks until he reaches the wooden door. He picks the key up off the floor, unlocks the door, opens the door, goes through the door, locks the door, and puts the key back on the floor. And then he walks and he walks and he walks and he walks and he walks and he walks and he walks until he reaches the metal door. He picks the key up off the floor, unlocks the door, opens the door, goes through the door, locks the door, and puts the key back on the floor. Then he walks and he walks and he walks and he walks and he walks and he walks and he walks over the two green hills until he reaches the purple gorilla.
He reaches in and pokes it. The gorilla starts going crazy in the cage. It starts thrashing about before suddenly breaking it open. So the man turns and he runs and he runs and he runs and he runs and he runs and he runs and he runs and he runs and he runs and he runs and he runs over the two green hills. He reaches the metal door, and he picks the key up off the floor, unlocks the door, opens the door, goes through the door, closes the door, locks the door, and puts the key back on the floor. He starts walking away, thinking there's no way the gorilla can get through a metal door, before he hears a 'BOOM' behind him.
The gorilla broke down the door! So he runs and he runs and he runs and he runs and he runs and he runs and he runs and he runs until he reaches the wooden door. He pick the key up off the floor, unlocks the door, opens the door, and runs through it, figuring that the gorilla would be able to get through a wooden one. He runs and he runs and he runs and he runs and he runs and he runs and he runs and he runs and he runs and he runs until he gets to the stairs and he climbs and he climbs and he climbs and he climbs and he climbs and he climbs and he climbs and he climbs until he gets back to the living room. He slams the trapdoor shut, puts the rug on the floor, the table on the rug, the chairs up to the table, and the candlesticks on the table. He walks back to his room, hoping the gorilla wouldn't be able to get through. He goes in, and finds the purple gorilla in his room.
So he runs and he runs and he runs and he runs and he runs and he runs and he runs and he runs and he runs and he runs and he runs and he runs and he runs and he runs and he runs and he runs until he reaches his motorcycle, which has magically been refilled with gas. He gets on it and he rides and he rides and he rides and he rides and he rides and he rides and he rides and he rides and he rides and he rides and he rides and he rides until he reaches his truck, which has also been magically refilled with gas.
He gets in the truck and he drives and he drives and he drives and he drives and he drives and he drives and he drives and he drives and he drives and he drives and he drives and he drives and he drives and he drives and he drives until he runs out of gas. And he runs and runs and runs, with the gorilla still following... After a while, he starts to think, "This gorilla is going to chase me until I die. I might as well stop and let him catch me." So he slows down and comes to a stop, turning to face it. It still runs towards him, but slows down once it notices the man has stopped. Finally, it walks up to the man, taps his shoulder, and says, "You're it."