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1.
The inability to produce any coherant thought pattern. Often a side effect of, but definitely not limited to, alcohol or drug consumption.
I don't know what happened last night, but i sure as hell am feeling scatterbrained this morning!
by da_sbpiyda March 03, 2004
 
2.
Disorganized, all over the place. Making numerous mistakes because your mind is on too many things at once and consequently none at all.
"Oh man! I figured out my finances wrong and overspent, then it turned out I bought the wrong thing and it'll be too late to return for an exchange. Then later I remembered I was supposed to meet somebody for coffee. I totally forgot."

"Man, you need to slow down. You're overworked and overwhelmed and you've become scatterbrained!"
by DeeDeeLee December 04, 2012