To have a leak in your attic
I came across the following phrase yesterday. It's a somewhat old phrase which we no longer use these days.
Context: The guy definitely has a leak in his attic. Make sure you go in there with a policeman.
I'd appreciate some insights into the meaning of the phrase.
This is not a common phrase and I doubt ever was but as @Gnawme and @SteveLovell point out, given the context, it's clearly one of a class of euphemisms that suggest that someone is insane. "Toys in the attic" is a similar phrase that is more common.