Face but no head
An idiot who acts like they’re smart, but they’re not. They’re face but no head, like a brainless idiot with a face.
"He’s face but no head, like he’s a brainless taco who thinks he’s smart.", @tacoidiot
"She’s face but no head, like a face with no brain who thinks she’s a genius.", @geniusfacehead
"That guy is face but no head, like he’s a brainless dummy who thinks he’s a king.", @dummyking2021"