Peanuts

Sam went to visit his grandma in the nursing home, they sat and talked about old times. Sam noticed a bowl of peanuts on the coffee table, so he helped himself during his discussion with his grandma. In the middle of grandma's toothless laugh, Sam noticed that he had eaten the whole bowl of peanuts!

"Grandma", said Sam, "I ate your entire bowl of peanuts!"

"Sam", said Granmda, "That's okay, I don't eat the peanuts anyways, I just love to suck the chocolate off of them".

That's a classic. The way I remember it was a salesman trying to sell stuff to an old lady. She leaves the room, he gets hungry, and eats the peanuts. You know the rest.