His death wasn't funny. It was excruciatingly painful to hear him scream like that. Not, in, like, the emotional way in that I was upset that he died, but in that it actually hurt my ears.
His, 'silence, traitor', line is what gives me hope that there is more to Demyx than what meets the eye. Sora underestimated him, and that's what always made me think that Demyx wanted it that way.
Demyx might not like to fight, but that doesn't mean he isn't stupid. Playing weak to get Sora to underestimate him, and therefore become cocky, would be just the type of thing someone with sly cunning would think to do, if it meant getting rid of him.