Incompetent

Characters who ended up being disliked due to being unable to have the ability for competence. They are able to achieve their goals, and commonly makes the same mistakes that bungle, botch, hinder or screw up their plans. This is due to either acts of stupidity, arrogance, cowardly behavior, weak strength or poor planning on their behalf.

By definition. They are the opposite of Mary Sue, and barely if ever overlap.