Knocker
WordNet
noun
(1) A device (usually metal and ornamental) attached by a hinge to a door
(2) Either of two soft fleshy milk-secreting glandular organs on the chest of a woman
(3) One who disparages or belittles the worth of something
(4) A person who knocks (as seeking to gain admittance)
"Open the door and see who the knocker is"
(5) (Yiddish) a big shot who knows it and acts that way; a boastful immoderate person