The Practical Joker
When the Enterprise is attacked by three Romulan warbirds, it hides in a gaseous energy field. The cloud affects the computer and it begins to play practical jokes on the crew, like making glasses leak, silverware turn to rubber, and covering decks with ice. The highlight of this episode is when McCoy, Uhura, and Sulu get trapped in trekdoms very first malfunctioning holodeck. The insurance rates for those things must be murder!