Your grandson was rude to accept the money and not say thank you. His father was equally rude in not making him.
Bad manners; nothing to do with raging hormones.
I would try to speak to him once more, and if he is rude again, then simply stop giving him money; no recriminations, simply stop.
Harry and Meghan ‘royal’ tour of Nigeria.
Our Welfare State. Is it broken?
NHS U turn on trans terminology
Forgetting where you left your keys does not mean you are “losing it”