has the same meaning as "douchebag"; a stupid or oafish person. This word may have been derived from the language of crazy high school seniors, who thought it would be funny to call someone a "douchecrab" instead of "douchebag". The word may have also originated from drunken conversations, in which a heavily drunk person slurred the word "douchecrab" instead of "douchebag".
Luke, you are such a douchecrab. Hahahah!