Greg, that subject really needs a thread to itself! It's an expression that crops up surprisingly often in literature in various guises, e.g. "kiss my royal Irish arse". Historically, it seems to have been an ejaculation or epithet expressing astonishment, contempt or amusement, rather than a literal invitation to perform the osculum infamum; although it's possible that the expression was originally "borrowed" from the withches' sabbath alleged practice of kissing the Devil's bottom.

These days it is heard less frequently, although in the UK sitcom The Royle Family, the character Jim often appends the words "my arse" to a word or phrase to indicate ridicule, as in "dance tune my arse!".

Steve