bungler (n.)

"to work or act clumsily," 1520s, origin obscure. OED suggests imitative; perhaps a mix of boggle and bumble, or perhaps [Skeat] from a Scandinavian word akin to Swedish bangla "to work ineffectually," Old Swedish bunga "to strike" (related to German Bengel "cudgel," also "rude fellow"). Related: Bungled; bungling.