Yoko Ono: "Stairway to Abuse" (Installation, 1968)

From the catalog of her retrospective one-woman show at London's Indica Gallery three years later:

Stairway to Abuse was a painting hung so high up on the wall that that those who wished to see it had to climb up a ladder (which was positioned directly underneath the painting). Upon climbing the ladder, one saw what appeared to be a blank canvas with a magnifying glass attached. Upon closer inspection, the canvas wasn't blank -- there was writing on it. The writing was so small, however, that it required the magnifying glass to be read.

One by one, spectators would climb up the ladder, peer through the magnifying glass, mutter words of amazement, look through the magnifying glass again (as though they hadn't believed it the first time), then climb down the ladder slowly and thoughtfully.

The message, when legible under the glass, was as follows:

YOU IDIOT!
You'll do anything anybody tells
you to do, won't you? You'll even
climb up a ladder in an art gallery!
Don't you have anything better to do?

No wonder John loved her.