Bungler
/ˈbʌŋɡlər/
Definition 1 of 1
Pro Tip 1/3Negative Connotation
Implies a lack of skill and competence. 
In every group project, he was the bungler who jeopardized our success.
Pro Tip 2/3Often Inept
Used when mistakes are frequent, not just a one-time event. 
She didn't trust the bungler to handle the delicate negotiations.
Pro Tip 3/3Not Malicious
A bungler's actions are due to ineptitude, not intentional harm. 
Though a bungler at chores, he never meant to break the vase.