knucklehead
knuck-le-head
noun
A foolish, stupid, or clumsy person, often prone to making silly mistakes.
"Don't be such a knucklehead and pay attention!"
Thesaurus
Synonyms: lunkhead, dunce, dumbass, dunderhead, fuckhead, hammerhead, numskull, loggerhead, muttonhead, shithead, blockhead, bonehead