>>92130475cont.
The way I read the dismemberment scene is that, seeing a crown on something that was not his own head, his greed overcame his sense, and his desire for another crown was so great as to drive him to self-destruction, even if it was fatal.
I see the banquet as the ultimate proof of this interpretation. He is provided with great luxury and privilege, possibly being the eternal reward that accompanies the divine right of a king. But he rejects this luxury entirely, desiring only more crowns. When it is properly impressed upon him that he is powerless to obtain Agatha's crown, he is actually willing to settle for a folded napkin, something that has no possible significance other than the superficial resemblance to a crown.
His irrationality is further illustrated by the others, who now treat the crowns as trivial decoration. But he genuinely does not care at all, since he could very well remain at the banquet with his new crown, but to him, nothing else matters in the universe as long as he has his crown.