One who is apt to behave in a stupid, silly, or scatterbrained manner. Did I really forget my wallet at home? I can be such a ditz sometimes. Oh, she's a ditz all right—she just said that two plus two is seven.
ditzand ditzo (dɪts(o))
n. a giddy, absent-minded person. I’m getting to be such a ditz! What a ditzo!