Dead from the neck up

British Slang

Definition

An insulting way to say someone is very stupid or dim-witted; lacking intelligence or common sense.

Examples

"I tried explaining it three times, but he’s dead from the neck up, isn’t he?"

"Honestly, leaving the oven on all night—she’s dead from the neck up."

"After that daft stunt with the ladder, they proved they’re dead from the neck up."