The origins of this one begin, and probably end, with my cousin. "There once was a man by the name of Jed, Went for a wank in a garden shed, Spunk bubbles like a black man's toothpaste" Sung to the tune of The Beverly Hillbillies.

Actually, there was loads more to it than that just spunk bubbles like a black man's toothpaste;

Let me tell you a story 'bout a man named Jed,
Couldn't find a toilet so he went behind a shed,
Couldn't find the bogroll so he used a bit of grass,Up popped Ellie May and shot him in the ass.
Next thing you know old Jed's in bed,

Wanking himself till his balls turned red,
erm, can't remember the rest rumtitum...
Next thing you know old Jed's a millionaire,
Selling condoms at 2p a pair,
2p, 4p, even two bob,
It all depends on the size of your knob.
Thank you very much ladies and gentlemen.

A more complete version of the second verse runs as follows:

Next thing you know old Jed's in bed,
Beating his meat until his dick turns red,
The door swung open, and Granny came through,
He said "Come along granny, and have a wank too".

There was a very similar song about our amusingly incompetent Scoutmaster, also called Jed:

"Right" said Jed,
in the potting shed,
with a naked woman on his head,
with melting mars bars on her tits,
but Jed just sat there, doing shits.

This was expanded over the course of one scout camp until it had assumed Homeric proportions, but unfortunately I can only remember the first five lines.
The inspiration for this epic came from the contemporary popularity of the band 'Right Said Fred', the rumoured existence of mars bar parties (qv), and the fact that Jed was a cock. I mean, what kind of fool would just do poopy when he had a naked woman sitting on his head?