not the full shilling
Rather stupid or unintelligent; slightly crazy or unhinged. He's not the full shilling if he thinks that plan is going to work. Of course he's not the full shilling—he's wearing pajamas at the beach!
not the full shilling
BRITISH, INFORMALIf you say that someone is not the full shilling, you mean that they are stupid or crazy. We all thought he wasn't quite the full shilling because he was slow — slow at sums and slow at writing.
not the full shilling
not mentally alert or quick-thinking.