What does that old chestnut mean?
A stale joke, story, or saying, as in Dad keeps on telling
that old chestnut about how many psychiatrists it takes to change a
light bulb. This expression comes from William Dimond's play,
The Broken Sword (1816), in which one character keeps
repeating the same stories, one of them about a cork tree, and is
interrupted each time by another character who says "Chestnut, you
mean . . . I have heard you tell the joke twenty-seven times and I
am sure it was a chestnut."