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

1.
bête comme ses pieds, idiot comme un balai
very stupid
:
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He's (as) thick as two short planks, he never understands anything.
Il est bête comme ses pieds, il ne comprend jamais rien.
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You'd have to be as thick as two short planks to believe that story.
Il faudrait être bête comme ses pieds pour croire cette histoire.