The extended Kubla Khan joke in Sourcery. It’s one of my favorite poems and I was howling to tears at a bus stop when I read it. People looked at me funny.
Million-to-one chances happen nine times out of ten.
I can’t find the exact quote, so this is from memory ( so I’m sure I’m butchering it ). “If you are ever held under the threat of death, pray it is by an evil man. An evil man will humiliate and torment you in order to prove his superiority, which gives you time to escape or be rescued. A good man will kill you with barely a word.”
And later on Carrot kills the evil man in question, with barely a word. Full circle.
and also from Men at Arms (paraphrased from memory)
*Anyone can pull a sword from a stone. It’s the man who puts the sword in the stone in the first place that you have to worry about.
*
and when Carrot kills the above evil man, he shoves the sword through his chest and deep into a granite column…
Si
Probably because of Quantum*.
- explains almost anything
“I smote him mightily!”
In certain conversations I’ve had of late, I find myself easily able to paraphrase Casanunda’s words. The fact that my interlocutor never fails to get the reference is merely a bonus.
“I sweat so much I’m going to have to change my vest any day now!”
It takes a very special and strong-minded kind of atheist to jump up and down with their hand clasped under their other armpit and shout, ‘Oh, random-fluctuations-in-the-space-time-continuum!’ or ‘Aaargh, primitive-and-outmoded-concept on a crutch!’
“Kubla Khan”? I thought it was about Omar Khayyam’s “Rubaiyat”!
There are references to both - there’s the book-of-verses, wilderness-is-paradise-enow business from the Ruba’iya’t but also the twice-five-miles something-or-other from Kubla Khan.
DROP THE SCYTHE, AND TURN AROUND SLOWLY. - DEATH goes all Clint Eastwood (Reaper Man)
…WE MUST CARE. FOR IF WE DO NOT CARE, WE DO NOT EXIST. IF WE DO NOT EXIST, THEN THERE IS NOTHING BUT BLIND OBLIVION. - DEATH, again. Reaper Man again
Millenium hand and shrimp!
Buggerit!
Maybe because it was Mightily Oats in Carpe Jugulum who said that. 
I always enjoy the references to Granny Weatherwax “happening to” someone.
“There are hardly any excesses of the most crazed psychopath that cannot easily be duplicated by a normal kindly family man who just comes in to work every day and has a job to do.” - Small Gods
Not everyone gets to live up to their name that way. 