ditzy
Stupid, silly, or scatterbrained. Did I really forget my wallet at home? I can be so ditzy sometimes. Oh, she's ditzy all right—she just said that two plus two is seven.
ditsy
verbditzy
and ditsy (ˈdɪtsi)mod. giddy; unaware; flighty. You are such a ditzy geek! She’s not the ditsy blonde she appears to be.