Before my latest watching of this episode I agreed with you, arashi, but this time around I noticed that Barnabas was having a worse than usual night. He muffed his attack on Ruby Tate, so, unless he fished her out of the water, he had to go find another victim. On his way back to the mausoleum, he paused at Jeremiah's grave to express sympathy with the man he had killed. He had other things than table manners on his mind. He may not have wanted to acknowledge the presence of blood on his face, or maybe he even felt he should keep it there, as a badge of shame - a scarlet C for Cannibal.
I keep reading and hearing about the sexual aspect of vampires sucking the blood of their victims, but in the past few days I've been thinking a lot about the cannibalistic aspect. It must be simply mind-boggling to start seeing your fellow human beings as food.