lackwit
A person who thinks they're a genius but can't tell the difference between a genius and a goon.
He said he was a genius and then asked me what a goon was. I said 'a fool' and he said 'then you're a lackwit.'
She tried to explain a math problem and said 'it’s like a goon with a calculator.' I said 'you’re a lackwit.'
He thought he was a genius because he could spell 'genius' and didn’t know what it meant.