be (as) crazy as a soup sandwich

To be completely unhinged, out of control, or in an incoherent mental state. This guy's as crazy as a soup sandwich. Do you have any idea what he's babbling about? Something about a "purple noodle sky balloon"? After seeing how she screamed at her students for the slightest infraction, everyone is starting to think she's just crazy as a soup sandwich. I'm going to be crazy as a soup sandwich if I have to listen to any more of their incessant arguing!