Learn English – n expression for someone who often takes things too literally

E.g., if you use an idiom (in a context) like: "To throw the baby away with the bathwater." and your conversation partner says: "Huh, seems I don't have a baby/bathwater!" Also, when you explain the meaning of the idiom, the other guy will still say: "Oh, but I really don't have a baby/bathwater!"

Or say something sarcastic like: (context: excellent tennis player on his way to a match. Everyone knows he wants to and it will be easy for him to defeat his opponent. Yet, on their way (tennis player and friend in his car) to the court, they are stuck in traffic and there is no way the excellent tennis player can turn up at his match in time (which means he will be disqualified). He goes "well, I am glad, at least I don't need to get all changed and tired to play my tennis match now." On which the other guy says "But I thought you wanted to win the trophy? You could have easily beaten that other player!! Why did you say that?!"