hmmm... here's one I rather like....(I found it, but I 'tweaked' a couple of lines and added one)

An old couple was watching TV one evening, and the husband got up to go to the kitchen. He asked his wife if he could bring her anything. She told him to bring her some iced tea, but knowing that the years had taken their toll on his memory, she told him to write it down.

"I can remember iced tea," he protested.

"But I want sugar in my tea too," she told him, "so write it down."

He told her he could remember iced tea with sugar.

"I want a slice of lemon too." she said, "Just write it down."

"I don't NEED to write it down," he replied. "I can remember iced tea with sugar & lemon!"

He left the room grumbling to himself. A few minutes later he came back with a plate full of mashed potatoes for her.

"I told you to write it down", she yelled at him, "See? You forgot the gravy!"