While I never actually planned any of it, some of the PC's ended up waging a prank war. It ended shortly after the enlisted engineer's (holographic) clothing vanished with the closing of the turbolift doors, by the way this was right in front of the Head of Security.
Another event was when the same engineer organized an “Enlisted Skip Day” while the ship was visiting a pirate port hidden in an asteroid field. The actual goal of the mission was to re-supply the ship and try and gather some decoy equipment for a dart across Cardassian/Dominion controlled space. As punishment, she was field promoted to Yeoman never again having the time to plan mayhem under the watchful eyes of the bridge crew.