The quest involved finding Prince Richard, supposedly being held captive by a Necromancer. As the party realised after killing the Necromancer, Prince Richard was not in his lair, but instead being held in a cage by a young brass dragon, and made to sing incessantly. As I narrated, I began to sing the song he was singing.... 'Never gonna give you up, never gonna let you down...'
And that is how I rickrolled an orc, a pseudodragon, and a handful of elves. Nevermind that the way to get Prince Rick back from the dragon was to give the dragon back his 'teddy', a large brown bear the party had just rescued from Hobgoblin Fight Club and set loose outside the dungeon, because they went around the dungeon bass-ackwards and didn't know that they would need the bear later. At that point, I let them get the bear back easily because after a 12-hour-long dungeon, I wasn't really going to be mean enough to make them hunt for it.