Essentially, a griefer is just a jerk whose parents never really corrected their behavior as children. ADHD and excuses made by the parent on their behalf is simply ex post facto justification of the parents' failure to raise a respectable and productive member of society.
I love the spin thrown on it there. Because I was such a failure as a parent, my child if far better equipped to do things that other people loathe. Whatever. He can help it. Just like "Bipolar" people can't control their behavior. Sure they can, but why should they? People just go "oh... he/she is bipolar, I understand." Bipolar is just a medically sanctioned excuse to act like a jerk all the time too. It rates right up there with ADHD, as medical excuses for immature behavior go.