Forget Me Not.
Ethel and Herman Rosenbaum both just turned 90 and they were becoming worried that they were losing their memories. They visited a doctor who assured them there was nothing seriously wrong except old age. He suggested that they both carry a notebook and write things down so that they wouldn't forget.
Several days later, Herman got up to go to the kitchen. Ethel said, "Dear, get me a bowl of ice cream while you're up."
"Okay," Herman said.
"...and put some chocolate syrup on it and a few cherries, too," Ethel added. "You'd better write all this down."
"I won't forget!" Herman said.
Twenty minutes later Herman came back into the room and handed his wife a plate of scrambled eggs. Ethel glared at him. "Now, I told you to write it down! I knew you'd forget."
"What did I forget?" Herman asked.
Ethel replied, "My toast!"