Showing once again that the "experts" are just as bad as the behavior they are attempting to justify, we see a report from the New York Post, which provides two headlines for one story, one on their front page, and one slightly different on the article page itself. Both are laughable. ...
In earliest uses the implication is of an unwanted or unplanned child rather than a reference to behavior; differing from a bastard in that a married couple might have a brat. From the association of brats belonging to low-class people evolved the sense "uncouth, ill-mannered child" by 1808...