When Goldeneyes Silverhand Dactylos dies. An awesome character, with an amazing backstory and being a friggin' cyborg to boot... and he doesn't survive more than three pages. Thanks for that kick in the balls, Pratchett!
The 2008 TV film
Rincewind being expelled from Unseen University, and attempting to jump into the River Ankh. Fortunately, it doesn't stick as soon as he's saved by an empty pallet and spots The Luggage.
Rincewind breaking the news to Twoflower that he was Only in It for the Money all along and telling Twoflower he never really cared about him. Twoflower looks absolutely crushed by this