be a cold fish

To show little to no emotion in a way that comes across as unfriendly or disinterested. The manager decided not to hire Sarah as a store greeter because she was a cold fish during the interview. He said he had a great time on our date, so why was he being a cold fish the whole time? I just can't understand people sometimes. I can't believe he teaches little kids—he always acts like such a cold fish whenever I'm around him.