An idiot; one who seems to have shit instead of brains, thus severely limiting their thought capacity.

1. Stupid. Careless.

2. A person evincing these characteristics.

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.

A shit for brains is usually heavily retarded, or this is this a gross understatement? My 40 year old sister thinks that electric cookers run off gas and she doesn't have a clue how much anything is at Poundland. She isn't just thick, she has shit for brains. Fancy calling your kids Skip? Toad? Soil? and Dildo? Fucking stupid shit for brains bitch Notwithstanding, she has very recently learnt to write her own name. Need I say more? She's a shit for brains. She's an ass wipe. She's a lude crude rude bag of pre chewed food, dude. She has the only house that you are more likely to slip on a turd inside, than outside in the street. Shit for brains also live in shit and furthermore never clean the toilet.

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.

common lexicon for someone who demonstrates a complete lack of intelligence or savoir faire ...

A stupid person, does not actualy refer to anyone actualy having shit in their skull.