It's gotta be Pol Pot.
His regime was the definition of society suicide.
Stalin comes in a close second due to the fact that there was nothing anybody could do to avoid being a target of his regime but at least his power grab wasn't so crazy that other Communist nations would need to intervene to stop him.
... and much to the annoyance of the United States.
Anyway by that point the communist world was hardly united in any way, if it ever was. Except of course in the imaginations of the CIA.
Anyway actually I agree with Tweed to a certain extent. But what he is talking about was already there under Lenin.