Im gonna wash that man right outta my hair

Im gonna wash that man right outta my hair is another way of saying that you are going to get rid of someones presence, tight down to the scent they have left behind. By saying you are getting him out of your house, you are saying that you want everything about him out of your life. This can pertain to his smell being left behind on you and in your hair or if he touched your hair with his hands, to wash those memories away.