Someone who makes mistakes because of incompetence.

synonyms: blunderer, botcher, bumbler, bungler, butcher, fuckup, sad sack, stumbler.

Roget 701: bungler; blunderer, blunderhead^†; marplot, fumbler, lubber, duffer, dauber, stick; bad hand, poor hand, poor shot; butterfingers^†.    no conjurer, flat, muff, slow coach, looby^†, lubber, swab; clod, yokel, awkward squad, blanc-bec; galoot^†.    land lubber; fresh water sailor, fair weather sailor; horse marine; fish out of water, ass in lion's skin, jackdaw in peacock's feathers; quack etc. (deceiver) 548; lord of misrule.    sloven, slattern, trapes^†.    amateur, novice, greenhorn (learner) 541.    ... show more

Dutch: stumper, prutser, stoethaspel, sukkel, blunderaar, knoeier, klungelaar, kluns, klungel, beunhaas, roffelaar ... show more
Polish: brakorób, brakoróbca, fuszer, niedbaluch, partacz