Yusei is a drink milk straight of the carton man. He wakes up, goes down to the kitchen and takes a sip of milk. Everytime he does so, Jack yells at him to just use a glass.
Yusei is the reason there tends to be no milk left at all. He’ll finish off a carton and forget to buy more because he’s working or working on an engine. Again, Jack is mad because he has no milk for his coffee or cereal.