lackwit
A brainless blob who thinks they're smart. Like a donut with no filling and no idea what a filling is.
My cousin tried to explain quantum physics and said 'it's like a donut' and that was it.
He asked me if I knew what a joke was and I said 'no' and he said 'then you're a lackwit'.
He tried to flirt with my dog and it stared at him like he was a bad pizza.