lummox
A clumsy, stupid person; an awkward bungler.
informal
You've broken the plates, you great lummox!
Where it comes from
Unknown. First attested in 1825 in East Anglian slang. Perhaps from "dumb ox", influenced by lumbering; or from or cognate to dialectal verb lummock (“move about heavily or clumsily”), itself a word of uncertain origin.
Adapted from the Wiktionary entry lummox (CC BY-SA 4.0).