cold fish

plural cold fishes

1. idiomaticpotentially endearingA heartless individual; a person lacking empathy and emotion.

   You're a cold fish. You have no heart.

   2003, Robert Wilson, The Blind Man of Seville, →ISBN, page 13

   2 more examples

   […]it was thought ſhe was a Woman, and was turn'd into a cold fiſh, for ſhe wold not exchange fleſh with one that lou'd her: […]

   c. 1610–1611 (date written), William Shakespeare, “The Winters Tale”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, →OCLC, [Act IV, scene iv], page 293, column 2

   He wouldn't have thought her such a cold fish. Pity. Still, there was plenty of time. Perhaps when she got used to his company she would thaw a little.

   1993, Lisanne Norman, Turning Point

   Synonyms: wet blanket, addle-plot, buzzkill, curmudgeon, dampener, downer, fun sponge, grinch

2. slangA sexual partner who, during sex, lacks vigor or emotional reciprocity.

   Synonyms: dead fish, starfish