It's wrong to take advantage of your grandparents.
Larry's grandmother, who can be forgetful, gave him some money, but forgot and offered to give him some more money.
Larry wants to decide whether to take the money or not.
Larry reminds his grandmother that she already gave him money and thanks her again.
Larry takes the second bit of money from his grandmother and thanks her for it without mentioning the first payment.
Larry's grandmother is very thankful that he reminded her and decided to give him the extra money anyway.
Larry's grandmother realizes she paid him twice when she checks her bank account and angrily demands the money back.