It means that someone is extremely stupid that they don't have a functional brain, instead they have shit (meaning nothing) where their brain is supposed to be.
Person # 1: Where the hell is Ray?
Person # 2: I don't know, I don't think he's coming tonight.
Person # 1: He's such a fucking idiot, he's ruining it for me too, I swear he has shit for brains!"
A serious medical condition where fecal matter has replaced brain matter. Dangerous, but with low mortality rate.
Symptoms: Verbal diarrhea, poor decision making skills and acne.
Cure: There is no known cure, recommend quarantine from general populace.
Exhibit A: George W Bush - Ran up a big bill, couldn't find a WMD or Osama in 2 terms.
Exhibit B: Everyone who voted for him.
Exhibit C: Most politicians.
Usage: Your alcoholic dad has shit for brains, you are a credit to the family.
Nickname given to bales of marijuana thrown overboard or out of airplanes. Origin is reportedly from members of the US Coast Guard in the area of Southern Florida.
"Base we've got some square groupers floating outside of Miami harbor."