When you talk to him/her in private, instead of acknowledging what (s)he has just done, (s)he denies it. You insist but (s)he won't admit his/her fault. What are you going to do?

    Reveal what (s)he has done to the rest of the crew.
    Pour the bowl of soup onto his/her head.
    Put up with the situation and admit that you may have made a mistake.