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!"
Slang for a way of ordering hashbrowns at The Waffle House diners. Scattered smothered and covered means that the hashbrowns are scattered on the grill, smothered with diced onions, and covered with melted cheese.
After a long night of drinking, you have to head down to The Waffle House at 3am and get em scattered smothered and covered.