"Three Older Ladies" joke

Three older ladies were discussing the problems of getting
older. One said, "Sometimes I catch myself with a jar of
mayonnaise in my hand, in front of the refrigerator, and can't
remember whether I need to put it away, or start making a
sandwich."
The second lady chimed in, "Yes, sometimes I find myself
standing on the stairs and can't remember whether I was on my
way up or on my way down."
The third one responded, " Well, I'm glad I don't have that
problem; knock on wood," as she rapped her knuckles on the
table... then said, "That must be the door, I'll get it!"