How about just not read his comments? Is it really so difficult to just go "Oh, it's Plasma's post, he annoys me, I won't read it." Because if you find his comments annoying, and you see he's posted.. and you choose to read it... then, at that point, you really have no one to blame but yourself.
The only reason Plasma posts continuously is because he's around 10 years old and he has absolutely nothing to do because, well...it's obvious that he has no friends. And this is what happens without adult supervision.