The Imperial College Union Bar version from 1969:

There once was a gay caballero
An exceedingly gay caballero
Who played with the end of his six-footed friend
An exceedingly gay caballero

He met a low-down signorita
An exceeding low-down signorita
Who played with the end of his six-footed friend
An exceeding low-down signorita

He contracted a low-down diseaso
An exceedingly low-down diseaso
That infected the end of his six-footed friend
An exceedingly low-down diseaso

He went to a low-down doctrino
An exceedingly low-down doctrino
Who cut off the end of his six-footed friend
An exceedingly low-down doctrino

There still lives a gay caballero
An exceedingly gay caballero
Who plays with the end of his four-footed friend
An exceedingly gay caballero

(There was a verse about a casino but I can't remember it. It's been fifty years, you know!)