sad sack(n = noun.person) blunderer, botcher, bumbler, bungler, butcher, fuckup, fumbler, stumbler - someone who makes mistakes because of incompetence;
is a kind of incompetent, incompetent person

dressing sack, give the sack, gunny sack, hit the sack, sack, sack coat, sack out, sack race, sack up, sad, sad case