From Longman Dictionary of Contemporary Englishcold fishcold fishUNFRIENDLYan unfriendly person who seems to have no strong feelings → fish
Examples from the Corpus
cold fish• Lord Halifax was a cold fish, a man of steely rectitude, a religious man.• They think we are cold fish and sloppy in our appearance.• Fancy standing back to the North Sea for ten hours or more handling cold fish!• I know people thought I was a real cold fish, but what could I do? 