Хе, това ми напомня други хубави фрази в същия/подобен смисъл:

He couldn't whittle a plug for a dog's ass with a pine knot for a pattern!
(тук се споменава "чеп")
He couldn't pour piss out of a boot if the instructions were written on the heel.
All foam, no beer.
He could fall in a barrel of tits and come out sucking his thumb.
He wouldn't know his ass from a hole in the ground.
He couldn't find his ass with a roadmap and a mirrior.
(He couldn't find his ass with both hands.)

Things are not as bad as they seem. They are worse.
Bill Press