the.com/cold fish

means A person who seems distant, unemotional, and hard to warm up to, especially in personal interactions.

from Built from a simple, old metaphor: fish are literally cold-blooded and slippery to the touch, so 'cold' plus 'fish' became shorthand for someone who feels similarly clammy and unresponsive in temperament. The phrase surfaces in English by the 19th century, riding on the much older habit of using fish imagery for unfeeling or shifty people — think also of 'slippery as an eel.' No single coiner or moment is recorded; it simply congealed out of everyday comparison.