Ship's fool
Ship's fool was a term for a person who was the butt of jokes, or fool, on a starship.
In 2374, after Alexander Rozhenko made the crew of the IKS Rotarran laugh at his mistaking a battle simulation for an actual attack, Martok assured Worf that his son was fitting in. Worf retorted that Alexander was the ship's fool. (DS9: "Sons and Daughters")