"Presbyophrenia" joke

Grandma & Grampa are sitting there watching TV when Grandpa decides
he's hungry for some ice cream.
"Hey, Grandma - I'm gonna' head to the kitchen and get myself a dish
of ice cream. You want I should get you some, too?"
"Sure, Grandpa, sounds good. But you better write down what you're
going out there for or else you'll forget." replies Grandma.
"I will not!" retorts Grandpa. "In fact, tell me what you want on it
and I'll show you I can remember that, too."
"OK," says Grandma, "I'll have some chocolate sauce. But you're
gonna' forget..."
Grandpa heads out to the kitchen and disappears for about 20 or 30
minutes, accompanied by a cacaphonous banging of pots and pans.
Finally he emerges, carrying a plate of scrambled eggs.
"See there, Grandpa. I told you you'd forget!" chides Grandma.
"Whaddya' mean, 'forget,' Grandma? What did I forget?" demands Grandpa.
"You fool," says Grandma. "You forgot my bacon!"