Version 1:

Picture a cowboy all dressed in red
Slipped on a boulder
Smashed in his head
Blood on the saddle
Blood on the ground
Great big blobs of blood all around
Great big blobs of greasy grimey gopher guts
Mutilated monkeys meat
Piggy's little hairy feet
Mix it up with violated vultures vomit
And eat it without a spoon
Yum Yum

(ed: Peter asks how do we remember these things from school days after ssssoooo many years??

Version 2:

Contributor says he remembers this from his childhood in the 1960's.

Picture a cowboy, all dressed in red
Slipped on a boulder, fractured his head
Blood on the saddle, blood on the ground
Great big gobs of blood all around!

.... and then you'd shout:

Second verse, same as the first!
A little bit louder and a little bit worse!

... and the more you sing it the louder you get until some adult yells at you to shut up. Great fun! (glad my kids don't know it ... yet.