They can be from any system, any adventure, funny or just plain wierd.
This was from my first game I ever DMed, I had the group start in a tavern (unoriginal I know). Most of the party was rangers or rogues. now I knew somethng was up, when they started asking what the tavern was made out of. I had created the innkeeper to play a part in the ending of the campaign, so he was strong. They managed to get him so angry, by trying to set fire to his establishment, and start bar fights. They all ran out of the Tavern, but the two rangers and the rogue, pinned the bard to the ground before leaving town, and the bard to her doom...