1) Bad hand 2) Blunderer 3) Blunderhead 4) Botcher 5) Bumbler 6) Butcher 7) Butterfingers 8) Clumsy workman 9) Dauber 10) Duffer 11) Fuckup 12) Fumbler 13) Incompetent 14) Incompetent person 15) Inept one 16) Lubber 17) Marplot 18) Poor hand 19) Poor shot 20) Sad sack 21) Stick 22) Stumbler 1) Blunderer 2) Botcher 3) Bumbler 4) Clod 5) Foul up 6) Fuckup 7) Fumbler 8) Mucker 
• (n.) A clumsy, awkward workman; one who bungles.
Bun'gler noun A clumsy, awkward workman; one who bungles. « If to be a dunce or a bungler in any profession be shameful, how much more ignominious and infamous to a scholar to be such! Barrow. » 
[n] - someone who makes mistakes because of incompetence
blunderer noun someone who makes mistakes because of incompetence