A "No" victim is a player who has played a "Just Say No!" card to reject an action that has been played against them. When this happens, the player that played the action (the "initiator) card has a chance to play their own "Just Say No!" card. If the victim quits the game before the initiator has made this decision, then the initiator will break the game if they do use their "Just Say No!" card.
To fix this, the victim needs to be prevented from quitting the game until the entire action has completed.