1) A cute way of calling someone Dumb.
2) A person who's sometime marked by extreme irrationality and superfluous illogicality.
3) A cute way of addressing your loved one.
a more brilliant way of saying that something is dumb-ish or someone is. dum-dum is "dumb" only that the b-sound is depleted and the new formed word is repeated twice to accent the state of being.