Descriptive of a person or persons who has the untold misfortune of having their entire head consisting of mostly faeces from unknown origin simply because they may have committed a crime against common sense.
"Charles your only supposed to use 20 grams of TNT not 200 you bloody poopoohead"
an insult you would most likely describe your sibling to not get in trouble with your mum. it means that that the person head is full of poop and they are stupid