The narrator, the narrator's wife, Robert
Again, the narrator is the clear antagonist of the story. He's his own worst enemy, and has the potential to hurt his wife and Robert deeply at the dinner party. Robert and the narrator's wife fit also this role as well. Their relationship antagonizes the narrator and they have the ability to hurt him through their relationship. When we first meet the narrator and his wife, they seem very antagonistic toward each other. He baits her by making fun of Robert's blindness, and she mistrusts him and speaks to him roughly. At the dinner party, each person has the power to damage the other two badly. Luckily, there aren't any real antagonists in the story. The characters are all pretty nice to each other in the final analysis.