Someone highly unsensible. A highly annoying person. A babbling idiot.
You're a blithering idiot
Basically, James May and Richard Hammond when they talk to Jermey Clarkson
Hammond you blithering idiot, you totally ruined this car!
Someone babbling like a bumbling band of baboons while being highly unaware of the situation.
Argus: "Students out of bed! Students in the corridors!"
Minerva: "They are supposed to be out of bed you blithering idiot!"
DJT: *Says words*
Almost everyone: "There's a blithering idiot if ever we saw one!"
A "blithering idiot" is someone who is somehow more stupid than stupid.
"Why is part of my cake missing?"
"Why'd you put it there in the first bloody place?"
" It was meant to be there, you blithering idiot!"