thick as mince

(as) thick as mince

slang Remarkably stupid, dimwitted, or obtuse. Primarily heard in UK. Jen's new girlfriend is very nice, but she's thick as mince. The MP was caught on a hot mic calling his colleague "as thick as mince."
See also: mince, thick
Farlex Dictionary of Idioms.

thick as mince

mainly SCOTTISH
If someone is as thick as mince, they are very stupid. No point in expecting any real help from her department — most of them are as thick as mince. Well, what do you expect? She's as thick as mince.
See also: mince, thick
Collins COBUILD Idioms Dictionary, 3rd ed.
See also:
  • (as) thick as mince
  • mince
  • be (as) thick as a brick
  • be (as) thick as a short plank
  • (as) thick as a brick
References in periodicals archive
This was newsworthy in itself but he got bigger headlines when he went on to describe Brexit Secretary David Davis, who is charged with negotiating our departure, as: "Thick as mince, lazy as a toad, and vain as Narcissus."
The Using English website says that someone who is thick as mince is "very stupid indeed".
Best insults have to be clever
TOTTI is known to be as thick as mince so it was no surprise he fell for a classic double bluff last weekend when missing a penalty in a 3-0 win over Reggina.
Football: Mince 'n Totti; World of FOOTBALL
SORRY for being so blunt but when I read the letter from one of your readers regarding the policing of the Barras, the saying "thick as mince" came to mind.
Your view: Thick as mince
One nurse stormed: "It proves they're as thick as mince.
ANGELS' 18p MINCE PIE XMAS BONUS