I'm reminded of this formula for 'not very bright':
'He's {number}{noun} short of a {related noun}', e.g.
'He's a few sandwiches short of a picnic...'
'He's a couple of cans short of a six-pack...'
'He's a few fries short of a Happy Meal...'
'He's a modal verb short of a CGEL...'
MrP
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