He's bound to fail the exam – he's thick as mince.
Examples of 'thick as mince' in a sentence
thick as mince
Sheep are still as thick as mince.
Times, Sunday Times (2018)
He got nabbed by a speed camera and a thick-as-mince district judge swallowed his story.
Times, Sunday Times (2006)
And congratulations to them, too, for giving us all hope by showing that they're really as thick as mince.
The Sun (2017)
Low-rent gangsters dispatched from a pariah, lowrent gangster state - where some of their primitive, thick-as-mince politicians have applauded the acts of violence.