When an undeveloped, boorish individual, often of black heritage, with a personality disorder, is trying to fit in with other undeveloped, boorish black individuals, they often repeat this phrase.
Also could mean when a black person is trying to give a present to another black person; a present in the shape of either plain shit, or moving shit (a niglet)
A mixture of shithead and idiot. Often known for as being an insult, definately not a compliment, and NOT defined by the following person above/below/whatever, it was a common swear word my grandfather would say when driving on the road and running across a 'shidiot' who obviously didn't know what they were doing.
That stupid shidiot doesn't know how to drive! The light isn't going to get any greener, damnit!