cold as a mackerel

adjective

1. not comparable Very cold (in temperature, emotionally, etc.). 1920, Fire Service (Official organ of the Fire Marshals’ Association of North America, and Eastern Association of Superintendents of Fire and Police Telegraph), 6 March, 1920, p. 7, “I tell you, Governor, that in those days they weren’t ashamed to have a little good liquor around to warm the insides
2. not comparable Completely unconscious. She had just slid forward in a pile in front of the chair, on top of her nice hat. She was as cold as a mackerel.