Familiar Ground

Have you ever held back character information from the rest of the party for some reason and it lead to an amusing or memorable moment?

I remember one time I was playing with someone who has never played D&D before. The experienced players noticed the overly clean dungeon and groaned when the expected gelatinous cube made its appearance.

Everyone seemed to have a silent understanding and nobody spoiled what was about to happen to the newbie, and sure enough, he ends up paralyzed and engulfed.

Everyone needs to have a first time experience with a gelatinous cube imo. There were also kobolds in that dungeon. Unfortunately, there were no ten foot pits, so the newbie trifecta of first level hazards was not achieved.