a person who makes statements that lack common sense.
DO NOT GET IT CONFUSED WITH A DUMB-DUMB.
Paris Hilton, Britney Spears, Lindsey Lohan, The Situation, Belinda Barbosa, Sarah Imhoff are all ding-dongs!
A person who lacks both intelligence and common sense.
These people are worthless most of the time.
Candy from Two and a Half Men is such a dum-dum.
Ditzy people are all dum-dums.