(as) thick as two short planks
US /əz θɪk əz tuː ʃɔrt plæŋks/
UK /əz θɪk əz tuː ʃɔrt plæŋks/

1.
笨得要命, 愚蠢至極
very stupid
:
•
He's (as) thick as two short planks, he never understands anything.
他笨得要命,什麼都聽不懂。
•
You'd have to be as thick as two short planks to believe that story.
你得笨到家了才會相信那個故事。