He acts like he is a few sandwiches short of a picnic.
short of a sheet
idiom Slang
Cockney rhyming slang · East London
in the street
Origin
Implying a situation of penury and hence the lack of a bed.
I think he is a few sandwiches short of a picnic because he tried to fix the sink with duct tape.
The villagers whispered that the eccentric inventor was a few sandwiches short of a picnic, given his strange habit of talking to the birds.