A cold fish negative noun phrase informal
I cannot understand why the boss let such a cold fish like Tom go to meet the partner.
Although Kenny looks like kind of a cold fish, he often helps others.
Jen must be a cold fish. She was always serious and rarely smiled at anyone.
To give no interest or attention to someone or something; to believe that something isn't important
Something that someone does not like.
It derived from William Shakespeare's The Winter's Tale in scene 4: "It was thought she was a woman and was turned into a cold fish" (Source: Wikipedia)