Definitions by E.E.Evans-Pritchard

solid as a soup sandwich 

Describes a person who was once trustworthy, but is no longer so, or someone who is simply untrustworthy.

The person is un-solid, much like the soup sandwich.

That guy was suppose to pay me my 20$ today, but he didn't even answer his door. He's as solid as a soup sandwich.

solid as a soup sandwich by E.E.Evans-Pritchard January 26, 2011