Years and years before she went and broke up one of the most expensive pop bands in history, Yoko Ono was a conceptual artist!
Here's some of her early "instruction poems":
PAINTING TO BE CONSTRUCTED IN YOUR HEAD
Observe three paintings carefully.
Mix them well in your head.
When the curtain rises, go hide
and wait until everybody leaves
Come out and play.
Hide until everybody goes home.
Hide until everybody forgets about you.
Hide until everybody dies.