From Discworld & Terry Pratchett Wiki
The Hedgehog Can Never be Buggered at All, more commonly known as The Hedgehog Song, is one of Discworld's most famous drinking songs. First mentioned in Wyrd Sisters, then referred to in Witches Abroad, some lyrics are mentioned, but due to the song's adult subject matter (spanning at least seventeen verses) the full version has not been printed. All that can be known is that in regards to certain interactions between humans and animals, the hedgehog is a most fortunate creature.
In the books, the song is associated with Nanny Ogg, who frequently sings it while intoxicated.
The UK paperback edition of Witches Abroad is dedicated "to all those people - and why not? - who, after the publication of Wyrd Sisters, deluged the author with their version of the words of 'The Hedgehog Song'. Deary deary me..."
Speaking of which, several versions of this song can be found around the internet, but the version on Lspace has been "streamlined and expanded by readers of the newsgroup and the L-Space Web site." This is a classic example of a Filk.