My dad says this all the time. He'll also respond with "Yes, someone to pay the bill," if asked if he needs anything else, and will say "Well, I guess it's free!" if something doesn't ring up right. (I hate, hate, HATE, that last one after hearing it 30 times a day everyday working retail!)
He never expects someone else to pay for his stuff, to bring someone to pay his bill, or to get anything for free. He is trying to make light of the situation, but he is not being a special snowflake, I promise. OP, I'm sorry you weren't in the mood for it, and I do understand that the "joke" isn't particularly funny, but it's also not an SS situation.